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<!DOCTYPE html>
<html class="ocks-org do-not-copy">
<head>
<meta charset="utf-8">
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<title>Comprehensive Python Cheatsheet</title>
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<body>
<header>
<aside>March 14, 2018</aside>
<a href="../" rel="author">Jure Šorn</a>
</header>
<h1 id="comprehensivepythoncheatsheet">Comprehensive Python Cheatsheet</h1>
<p class="banner"><sup><a href="https://raw.githubusercontent.com/gto76/python-cheatsheet/master/README.md">Download text file</a>, <a href="https://github.com/gto76/python-cheatsheet">Fork me on GitHub</a> or <a href="https://github.com/gto76/python-cheatsheet/wiki/Frequently-Asked-Questions">Check out FAQ</a>.
</sup></p>
<p class="banner"><img src="web/image_888.jpeg" alt="Monty Python"></p>
<br><h2 id="toc"><a href="#toc" name="toc">#</a>Contents</h2>
<pre><code class="hljs bash"><strong>ToC</strong> = {
<strong><span class="hljs-string"><span class="hljs-string">'1. Collections'</span></span></strong>: [<a href="#list">List</a>, <a href="#dictionary">Dict</a>, <a href="#set">Set</a>, <a href="#range">Range</a>, <a href="#enumerate">Enumerate</a>, <a href="#namedtuple">Namedtuple</a>, <a href="#iterator">Iterator</a>, <a href="#generator">Generator</a>],
<strong><span class="hljs-string"><span class="hljs-string">'2. Types'</span></span></strong>: [<a href="#type">Type</a>, <a href="#string">String</a>, <a href="#regex">Regex</a>, <a href="#format">Format</a>, <a href="#numbers">Numbers</a>, <a href="#combinatorics">Combinatorics</a>, <a href="#datetime">Datetime</a>ᴺᴱᵂ],
<strong><span class="hljs-string"><span class="hljs-string">'3. Syntax'</span></span></strong>: [<a href="#arguments">Arguments</a>, <a href="#splatoperator">Splat</a>, <a href="#inline">Inline</a>, <a href="#closure">Closure</a>, <a href="#decorator">Decorator</a>, <a href="#class">Class</a>, <a href="#enum">Enum</a>, <a href="#exceptions">Exceptions</a>],
<strong><span class="hljs-string"><span class="hljs-string">'4. System'</span></span></strong>: [<a href="#print">Print</a>, <a href="#input">Input</a>, <a href="#commandlinearguments">Command_Line_Arguments</a>, <a href="#open">Open</a>, <a href="#path">Path</a>ᴺᴱᵂ, <a href="#commandexecution">Command_Execution</a>],
<strong><span class="hljs-string"><span class="hljs-string">'5. Data'</span></span></strong>: [<a href="#csv">CSV</a>, <a href="#json">JSON</a>, <a href="#pickle">Pickle</a>, <a href="#sqlite">SQLite</a>, <a href="#bytes">Bytes</a>, <a href="#struct">Struct</a>, <a href="#array">Array</a>, <a href="#memoryview">MemoryView</a>, <a href="#deque">Deque</a>],
<strong><span class="hljs-string"><span class="hljs-string">'6. Advanced'</span></span></strong>: [<a href="#threading">Threading</a>, <a href="#introspection">Introspection</a>, <a href="#metaprograming">Metaprograming</a>, <a href="#operator">Operator</a>, <a href="#eval">Eval</a>, <a href="#coroutine">Coroutine</a>],
<strong><span class="hljs-string"><span class="hljs-string">'7. Libraries'</span></span></strong>: [<a href="#progressbar">Progress_Bar</a>, <a href="#plot">Plot</a>, <a href="#table">Table</a>, <a href="#curses">Curses</a>, <a href="#logging">Logging</a>ᴺᴱᵂ, <a href="#scraping">Scraping</a>, <a href="#web">Web</a>, <a href="#profile">Profile</a>,
<a href="#numpy">NumPy</a>, <a href="#image">Image</a>, <a href="#audio">Audio</a>]
}
</code></pre>
<h2 id="main"><a href="#main" name="main">#</a>Main</h2>
<pre><code class="python language-python hljs"><span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span>: <span class="hljs-comment"># Runs main() if file wasn't imported.</span>
main()
</code></pre>
<h2 id="list"><a href="#list" name="list">#</a>List</h2>
<pre><code class="python language-python hljs"><list> = <list>[from_inclusive : to_exclusive : ±step_size]
</code></pre>
<pre><code class="python language-python hljs"><list>.append(<el>) <span class="hljs-comment"># Or: <list> += [<el>]</span>
<list>.extend(<collection>) <span class="hljs-comment"># Or: <list> += <collection></span>
</code></pre>
<pre><code class="python language-python hljs"><list>.sort()
<list>.reverse()
<list> = sorted(<collection>)
<iter> = reversed(<list>)
</code></pre>
<pre><code class="python language-python hljs">sum_of_elements = sum(<collection>)
elementwise_sum = [sum(pair) <span class="hljs-keyword">for</span> pair <span class="hljs-keyword">in</span> zip(list_a, list_b)]
sorted_by_second = sorted(<collection>, key=<span class="hljs-keyword">lambda</span> el: el[<span class="hljs-number">1</span>])
sorted_by_both = sorted(<collection>, key=<span class="hljs-keyword">lambda</span> el: (el[<span class="hljs-number">1</span>], el[<span class="hljs-number">0</span>]))
flatter_list = list(itertools.chain.from_iterable(<list>))
product_of_elems = functools.reduce(<span class="hljs-keyword">lambda</span> out, x: out * x, <collection>)
list_of_chars = list(<str>)
</code></pre>
<pre><code class="python language-python hljs">index = <list>.index(<el>) <span class="hljs-comment"># Returns first index of item.</span>
<list>.insert(index, <el>) <span class="hljs-comment"># Inserts item at index and moves the rest to the right.</span>
<el> = <list>.pop([index]) <span class="hljs-comment"># Removes and returns item at index or from the end.</span>
<list>.remove(<el>) <span class="hljs-comment"># Removes first occurrence of item or raises ValueError.</span>
<list>.clear() <span class="hljs-comment"># Removes all items.</span>
</code></pre>
<h2 id="dictionary"><a href="#dictionary" name="dictionary">#</a>Dictionary</h2>
<pre><code class="python language-python hljs"><view> = <dict>.keys() <span class="hljs-comment"># Coll. of keys that reflects changes.</span>
<view> = <dict>.values() <span class="hljs-comment"># Coll. of values that reflects changes.</span>
<view> = <dict>.items() <span class="hljs-comment"># Coll. of key-value tuples.</span>
</code></pre>
<pre><code class="python language-python hljs">value = <dict>.get(key, default=<span class="hljs-keyword">None</span>) <span class="hljs-comment"># Returns default if key does not exist.</span>
value = <dict>.setdefault(key, default=<span class="hljs-keyword">None</span>) <span class="hljs-comment"># Same, but also adds default to dict.</span>
<dict> = collections.defaultdict(<type>) <span class="hljs-comment"># Creates a dict with default value of type.</span>
<dict> = collections.defaultdict(<span class="hljs-keyword">lambda</span>: <span class="hljs-number">1</span>) <span class="hljs-comment"># Creates a dict with default value 1.</span>
</code></pre>
<pre><code class="python language-python hljs"><dict>.update(<dict>) <span class="hljs-comment"># Or: dict_a = {**dict_a, **dict_b}.</span>
<dict> = dict(<collection>) <span class="hljs-comment"># Creates a dict from coll. of key-value pairs.</span>
<dict> = dict(zip(keys, values)) <span class="hljs-comment"># Creates a dict from two collections.</span>
<dict> = dict.fromkeys(keys [, value]) <span class="hljs-comment"># Creates a dict from collection of keys.</span>
</code></pre>
<pre><code class="python language-python hljs">value = <dict>.pop(key) <span class="hljs-comment"># Removes item from dictionary.</span>
{k: v <span class="hljs-keyword">for</span> k, v <span class="hljs-keyword">in</span> <dict>.items() <span class="hljs-keyword">if</span> k <span class="hljs-keyword">in</span> keys} <span class="hljs-comment"># Filters dictionary by keys.</span>
</code></pre>
<h3 id="counter">Counter</h3>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> Counter
<span class="hljs-meta">>>> </span>colors = [<span class="hljs-string">'red'</span>, <span class="hljs-string">'blue'</span>, <span class="hljs-string">'yellow'</span>, <span class="hljs-string">'blue'</span>, <span class="hljs-string">'red'</span>, <span class="hljs-string">'blue'</span>]
<span class="hljs-meta">>>> </span>counter = Counter(colors)
Counter({<span class="hljs-string">'blue'</span>: <span class="hljs-number">3</span>, <span class="hljs-string">'red'</span>: <span class="hljs-number">2</span>, <span class="hljs-string">'yellow'</span>: <span class="hljs-number">1</span>})
<span class="hljs-meta">>>> </span>counter.most_common()[<span class="hljs-number">0</span>]
(<span class="hljs-string">'blue'</span>, <span class="hljs-number">3</span>)
</code></pre>
<h2 id="set"><a href="#set" name="set">#</a>Set</h2>
<pre><code class="python language-python hljs"><set> = set()
</code></pre>
<pre><code class="python language-python hljs"><set>.add(<el>) <span class="hljs-comment"># Or: <set> |= {<el>}</span>
<set>.update(<collection>) <span class="hljs-comment"># Or: <set> |= <set></span>
</code></pre>
<pre><code class="python language-python hljs"><set> = <set>.union(<coll.>) <span class="hljs-comment"># Or: <set> | <set></span>
<set> = <set>.intersection(<coll.>) <span class="hljs-comment"># Or: <set> & <set></span>
<set> = <set>.difference(<coll.>) <span class="hljs-comment"># Or: <set> - <set></span>
<set> = <set>.symmetric_difference(<coll.>) <span class="hljs-comment"># Or: <set> ^ <set></span>
<bool> = <set>.issubset(<coll.>) <span class="hljs-comment"># Or: <set> <= <set></span>
<bool> = <set>.issuperset(<coll.>) <span class="hljs-comment"># Or: <set> >= <set></span>
</code></pre>
<pre><code class="python language-python hljs"><set>.remove(<el>) <span class="hljs-comment"># Raises KeyError.</span>
<set>.discard(<el>) <span class="hljs-comment"># Doesn't raise an error.</span>
</code></pre>
<h3 id="frozenset">Frozenset</h3>
<h4 id="ishashablemeaningitcanbeusedasakeyinadictionaryorasanelementinaset">Is hashable, meaning it can be used as a key in a dictionary or as an element in a set.</h4>
<pre><code class="python language-python hljs"><frozenset> = frozenset(<collection>)
</code></pre>
<h2 id="range"><a href="#range" name="range">#</a>Range</h2>
<pre><code class="python language-python hljs"><range> = range(to_exclusive)
<range> = range(from_inclusive, to_exclusive)
<range> = range(from_inclusive, to_exclusive, ±step_size)
</code></pre>
<pre><code class="python language-python hljs">from_inclusive = <range>.start
to_exclusive = <range>.stop
</code></pre>
<h2 id="enumerate"><a href="#enumerate" name="enumerate">#</a>Enumerate</h2>
<pre><code class="python language-python hljs"><span class="hljs-keyword">for</span> i, el <span class="hljs-keyword">in</span> enumerate(<collection> [, i_start]):
...
</code></pre>
<h2 id="namedtuple"><a href="#namedtuple" name="namedtuple">#</a>Named Tuple</h2>
<ul>
<li><strong>Tuple is an immutable and hashable list.</strong></li>
<li><strong>Named tuple is its subclass with named elements.</strong></li>
</ul>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
<span class="hljs-meta">>>> </span>Point = namedtuple(<span class="hljs-string">'Point'</span>, <span class="hljs-string">'x y'</span>)
<span class="hljs-meta">>>> </span>p = Point(<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>)
Point(x=<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>)
<span class="hljs-meta">>>> </span>p[<span class="hljs-number">0</span>]
<span class="hljs-number">1</span>
<span class="hljs-meta">>>> </span>p.x
<span class="hljs-number">1</span>
<span class="hljs-meta">>>> </span>getattr(p, <span class="hljs-string">'y'</span>)
<span class="hljs-number">2</span>
<span class="hljs-meta">>>> </span>p._fields <span class="hljs-comment"># Or: Point._fields</span>
(<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>)
</code></pre>
<h2 id="iterator"><a href="#iterator" name="iterator">#</a>Iterator</h2>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> itertools <span class="hljs-keyword">import</span> count, repeat, cycle, chain, islice
</code></pre>
<pre><code class="python language-python hljs"><iter> = iter(<collection>)
<iter> = iter(<function>, to_exclusive) <span class="hljs-comment"># Sequence of return values until 'to_exclusive'.</span>
<el> = next(<iter> [, default]) <span class="hljs-comment"># Raises StopIteration or returns 'default' on end.</span>
</code></pre>
<pre><code class="python language-python hljs"><iter> = count(start=<span class="hljs-number">0</span>, step=<span class="hljs-number">1</span>) <span class="hljs-comment"># Returns incremented value endlessly.</span>
<iter> = repeat(<el> [, times]) <span class="hljs-comment"># Returns element endlessly or 'times' times.</span>
<iter> = cycle(<collection>) <span class="hljs-comment"># Repeats the sequence indefinitely.</span>
</code></pre>
<pre><code class="python language-python hljs"><iter> = chain(<coll.>, <coll.>, ...) <span class="hljs-comment"># Empties collections in order.</span>
<iter> = chain.from_iterable(<collection>) <span class="hljs-comment"># Empties collections inside a collection in order.</span>
</code></pre>
<pre><code class="python language-python hljs"><iter> = islice(<collection>, to_exclusive)
<iter> = islice(<collection>, from_inclusive, to_exclusive)
<iter> = islice(<collection>, from_inclusive, to_exclusive, step_size)
</code></pre>
<h2 id="generator"><a href="#generator" name="generator">#</a>Generator</h2>
<p><strong>Convenient way to implement the iterator protocol.</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">count</span><span class="hljs-params">(start, step)</span>:</span>
<span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
<span class="hljs-keyword">yield</span> start
start += step
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>counter = count(<span class="hljs-number">10</span>, <span class="hljs-number">2</span>)
<span class="hljs-meta">>>> </span>next(counter), next(counter), next(counter)
(<span class="hljs-number">10</span>, <span class="hljs-number">12</span>, <span class="hljs-number">14</span>)
</code></pre>
<h2 id="type"><a href="#type" name="type">#</a>Type</h2>
<pre><code class="python language-python hljs"><type> = type(<el>) <span class="hljs-comment"># <class 'int'> / <class 'str'> / ...</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> numbers <span class="hljs-keyword">import</span> Integral, Rational, Real, Complex, Number
<bool> = isinstance(<el>, Number)
</code></pre>
<pre><code class="python language-python hljs"><bool> = callable(<el>)
</code></pre>
<h2 id="string"><a href="#string" name="string">#</a>String</h2>
<pre><code class="python language-python hljs"><str> = <str>.strip() <span class="hljs-comment"># Strips all whitespace characters from both ends.</span>
<str> = <str>.strip(<span class="hljs-string">'<chars>'</span>) <span class="hljs-comment"># Strips all passed characters from both ends.</span>
</code></pre>
<pre><code class="python language-python hljs"><list> = <str>.split() <span class="hljs-comment"># Splits on any whitespace character.</span>
<list> = <str>.split(sep=<span class="hljs-keyword">None</span>, maxsplit=<span class="hljs-number">-1</span>) <span class="hljs-comment"># Splits on 'sep' str at most 'maxsplit' times.</span>
<str> = <str>.join(<collection>) <span class="hljs-comment"># Joins elements using string as separator.</span>
</code></pre>
<pre><code class="python language-python hljs"><str> = <str>.replace(old, new [, count]) <span class="hljs-comment"># Replaces 'old' with 'new' at most 'count' times.</span>
<bool> = <str>.startswith(<sub_str>) <span class="hljs-comment"># Pass tuple of strings for multiple options.</span>
<bool> = <str>.endswith(<sub_str>) <span class="hljs-comment"># Pass tuple of strings for multiple options.</span>
<int> = <str>.index(<sub_str>) <span class="hljs-comment"># Returns start index of first match.</span>
</code></pre>
<pre><code class="python language-python hljs"><bool> = <str>.isnumeric() <span class="hljs-comment"># True if str contains only numeric characters.</span>
<list> = textwrap.wrap(<str>, width) <span class="hljs-comment"># Nicely breaks string into lines.</span>
</code></pre>
<h3 id="char">Char</h3>
<pre><code class="python language-python hljs"><str> = chr(<int>) <span class="hljs-comment"># Converts int to unicode char.</span>
<int> = ord(<str>) <span class="hljs-comment"># Converts unicode char to int.</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>ord(<span class="hljs-string">'0'</span>), ord(<span class="hljs-string">'9'</span>)
(<span class="hljs-number">48</span>, <span class="hljs-number">57</span>)
<span class="hljs-meta">>>> </span>ord(<span class="hljs-string">'A'</span>), ord(<span class="hljs-string">'Z'</span>)
(<span class="hljs-number">65</span>, <span class="hljs-number">90</span>)
<span class="hljs-meta">>>> </span>ord(<span class="hljs-string">'a'</span>), ord(<span class="hljs-string">'z'</span>)
(<span class="hljs-number">97</span>, <span class="hljs-number">122</span>)
</code></pre>
<h2 id="regex"><a href="#regex" name="regex">#</a>Regex</h2>
<pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> re
<str> = re.sub(<regex>, new, text, count=<span class="hljs-number">0</span>) <span class="hljs-comment"># Substitutes all occurrences.</span>
<list> = re.findall(<regex>, text) <span class="hljs-comment"># Returns all occurrences.</span>
<list> = re.split(<regex>, text, maxsplit=<span class="hljs-number">0</span>) <span class="hljs-comment"># Use brackets in regex to keep the matches.</span>
<Match> = re.search(<regex>, text) <span class="hljs-comment"># Searches for first occurrence of pattern.</span>
<Match> = re.match(<regex>, text) <span class="hljs-comment"># Searches only at the beginning of the text.</span>
<iter> = re.finditer(<regex>, text) <span class="hljs-comment"># Returns all occurrences as match objects.</span>
</code></pre>
<ul>
<li><strong>Parameter <code class="python hljs"><span class="hljs-string">'flags=re.IGNORECASE'</span></code> can be used with all functions.</strong></li>
<li><strong>Parameter <code class="python hljs"><span class="hljs-string">'flags=re.DOTALL'</span></code> makes dot also accept newline.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">r'\1'</span></code> or <code class="python hljs"><span class="hljs-string">'\\1'</span></code> for backreference.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'?'</span></code> to make an operator non-greedy.</strong></li>
</ul>
<h3 id="matchobject">Match Object</h3>
<pre><code class="python language-python hljs"><str> = <Match>.group() <span class="hljs-comment"># Whole match.</span>
<str> = <Match>.group(<span class="hljs-number">1</span>) <span class="hljs-comment"># Part in first bracket.</span>
<tuple> = <Match>.groups() <span class="hljs-comment"># All bracketed parts.</span>
<int> = <Match>.start() <span class="hljs-comment"># Start index of a match.</span>
<int> = <Match>.end() <span class="hljs-comment"># Exclusive end index of a match.</span>
</code></pre>
<h3 id="specialsequences">Special Sequences</h3>
<p><strong>Expressions below hold true for strings that contain only ASCII characters. Use capital letters for negation.</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-string">'\d'</span> == <span class="hljs-string">'[0-9]'</span> <span class="hljs-comment"># Digit</span>
<span class="hljs-string">'\s'</span> == <span class="hljs-string">'[ \t\n\r\f\v]'</span> <span class="hljs-comment"># Whitespace</span>
<span class="hljs-string">'\w'</span> == <span class="hljs-string">'[a-zA-Z0-9_]'</span> <span class="hljs-comment"># Alphanumeric</span>
</code></pre>
<h2 id="format"><a href="#format" name="format">#</a>Format</h2>
<pre><code class="python language-python hljs"><str> = <span class="hljs-string">f'<span class="hljs-subst">{<el_1>}</span>, <span class="hljs-subst">{<el_2>}</span>'</span>
<str> = <span class="hljs-string">'{}, {}'</span>.format(<el_1>, <el_2>)
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
<span class="hljs-meta">>>> </span>Person = namedtuple(<span class="hljs-string">'Person'</span>, <span class="hljs-string">'name height'</span>)
<span class="hljs-meta">>>> </span>person = Person(<span class="hljs-string">'Jean-Luc'</span>, <span class="hljs-number">187</span>)
<span class="hljs-meta">>>> </span><span class="hljs-string">f'<span class="hljs-subst">{person.height}</span>'</span>
<span class="hljs-string">'187'</span>
<span class="hljs-meta">>>> </span><span class="hljs-string">'{p.height}'</span>.format(p=person)
<span class="hljs-string">'187'</span>
</code></pre>
<h3 id="generaloptions">General Options</h3>
<pre><code class="python language-python hljs">{<el>:<<span class="hljs-number">10</span>} <span class="hljs-comment"># '<el> '</span>
{<el>:><span class="hljs-number">10</span>} <span class="hljs-comment"># ' <el>'</span>
{<el>:^<span class="hljs-number">10</span>} <span class="hljs-comment"># ' <el> '</span>
{<el>:.><span class="hljs-number">10</span>} <span class="hljs-comment"># '......<el>'</span>
{<el>:><span class="hljs-number">0</span>} <span class="hljs-comment"># '<el>'</span>
</code></pre>
<h3 id="stringoptions">String Options</h3>
<p><strong><code class="python hljs"><span class="hljs-string">'!r'</span></code> calls object's repr() method, instead of format(), to get a string.</strong></p>
<pre><code class="python language-python hljs">{<span class="hljs-string">'abcde'</span>!r:<<span class="hljs-number">10</span>} <span class="hljs-comment"># "'abcde' "</span>
{<span class="hljs-string">'abcde'</span>:<span class="hljs-number">.3</span>} <span class="hljs-comment"># 'abc'</span>
{<span class="hljs-string">'abcde'</span>:<span class="hljs-number">10.3</span>} <span class="hljs-comment"># 'abc '</span>
</code></pre>
<h3 id="numberoptions">Number Options</h3>
<pre><code class="python language-python hljs">{ <span class="hljs-number">123456</span>:<span class="hljs-number">10</span>,} <span class="hljs-comment"># ' 123,456'</span>
{ <span class="hljs-number">123456</span>:<span class="hljs-number">10</span>_} <span class="hljs-comment"># ' 123_456'</span>
{ <span class="hljs-number">123456</span>:+<span class="hljs-number">10</span>} <span class="hljs-comment"># ' +123456'</span>
{<span class="hljs-number">-123456</span>:=<span class="hljs-number">10</span>} <span class="hljs-comment"># '- 123456'</span>
{ <span class="hljs-number">123456</span>: } <span class="hljs-comment"># ' 123456'</span>
{<span class="hljs-number">-123456</span>: } <span class="hljs-comment"># '-123456'</span>
</code></pre>
<h4 id="floattypes">Float types:</h4>
<pre><code class="python language-python hljs">{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>f} <span class="hljs-comment"># ' 1.235'</span>
{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>e} <span class="hljs-comment"># ' 1.235e+00'</span>
{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>%} <span class="hljs-comment"># ' 123.456%'</span>
</code></pre>
<h4 id="inttypes">Int types:</h4>
<pre><code class="python language-python hljs">{<span class="hljs-number">90</span>:c} <span class="hljs-comment"># 'Z'</span>
{<span class="hljs-number">90</span>:X} <span class="hljs-comment"># '5A'</span>
{<span class="hljs-number">90</span>:b} <span class="hljs-comment"># '1011010'</span>
</code></pre>
<h2 id="numbers"><a href="#numbers" name="numbers">#</a>Numbers</h2>
<h3 id="basicfunctions">Basic Functions</h3>
<pre><code class="python language-python hljs"><num> = pow(<num>, <num>) <span class="hljs-comment"># Or: <num> ** <num></span>
<real> = abs(<num>)
<int> = round(<real>)
<real> = round(<real>, ±ndigits)
</code></pre>
<h3 id="math">Math</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> e, pi
<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> cos, acos, sin, asin, tan, atan, degrees, radians
<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> log, log10, log2
<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> inf, nan, isinf, isnan
</code></pre>
<h3 id="statistics">Statistics</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> statistics <span class="hljs-keyword">import</span> mean, median, variance, pvariance, pstdev
</code></pre>
<h3 id="random">Random</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> random <span class="hljs-keyword">import</span> random, randint, choice, shuffle
<float> = random()
<int> = randint(from_inclusive, to_inclusive)
<el> = choice(<list>)
shuffle(<list>)
</code></pre>
<h2 id="combinatorics"><a href="#combinatorics" name="combinatorics">#</a>Combinatorics</h2>
<ul>
<li><strong>Every function returns an iterator.</strong></li>
<li><strong>If you want to print the iterator, you need to pass it to the list() function!</strong></li>
</ul>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> itertools <span class="hljs-keyword">import</span> product, combinations, combinations_with_replacement, permutations
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>product([<span class="hljs-number">0</span>, <span class="hljs-number">1</span>], repeat=<span class="hljs-number">3</span>)
[(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>), (<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">1</span>), (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">0</span>), (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>),
(<span class="hljs-number">1</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>), (<span class="hljs-number">1</span>, <span class="hljs-number">0</span>, <span class="hljs-number">1</span>), (<span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">0</span>), (<span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>)]
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>product(<span class="hljs-string">'ab'</span>, <span class="hljs-string">'12'</span>)
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'1'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'2'</span>),
(<span class="hljs-string">'b'</span>, <span class="hljs-string">'1'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'2'</span>)]
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>combinations(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>)
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>)]
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>combinations_with_replacement(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>)
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),
(<span class="hljs-string">'b'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>),
(<span class="hljs-string">'c'</span>, <span class="hljs-string">'c'</span>)]
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>permutations(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>)
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),
(<span class="hljs-string">'b'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>),
(<span class="hljs-string">'c'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'b'</span>)]
</code></pre>
<h2 id="datetime"><a href="#datetime" name="datetime">#</a>Datetime</h2>
<ul>
<li><strong>Module 'datetime' provides 'date' <code class="apache hljs"><span class="hljs-section"><D></span></code>, 'time' <code class="apache hljs"><span class="hljs-section"><T></span></code>, 'datetime' <code class="apache hljs"><span class="hljs-section"><DT></span></code> and 'timedelta' <code class="apache hljs"><span class="hljs-section"><TD></span></code> classes. All are immutable and hashable.</strong></li>
<li><strong>Time and datetime can be 'aware' <code class="apache hljs"><span class="hljs-section"><a></span></code>, meaning they have defined timezone, or 'naive' <code class="apache hljs"><span class="hljs-section"><n></span></code>, meaning they don't.</strong></li>
<li><strong>If object is naive it is presumed to be in system's timezone.</strong></li>
</ul>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> datetime <span class="hljs-keyword">import</span> date, time, datetime, timedelta
<span class="hljs-keyword">from</span> dateutil.tz <span class="hljs-keyword">import</span> UTC, tzlocal, gettz
</code></pre>
<h3 id="constructors">Constructors</h3>
<pre><code class="python language-python apache hljs"><D> = date(year, month, day)
<T> = time(hour=<span class="hljs-number">0</span>, minute=<span class="hljs-number">0</span>, second=<span class="hljs-number">0</span>, microsecond=<span class="hljs-number">0</span>, tzinfo=<span class="hljs-keyword">None</span>, fold=<span class="hljs-number">0</span>)
<DT> = datetime(year, month, day, hour=<span class="hljs-number">0</span>, minute=<span class="hljs-number">0</span>, second=<span class="hljs-number">0</span>, ...)
<TD> = timedelta(days=<span class="hljs-number">0</span>, seconds=<span class="hljs-number">0</span>, microseconds=<span class="hljs-number">0</span>, milliseconds=<span class="hljs-number">0</span>,
minutes=<span class="hljs-number">0</span>, hours=<span class="hljs-number">0</span>, weeks=<span class="hljs-number">0</span>)
</code></pre>
<ul>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'<D/DT>.weekday()'</span></code> to get the day of the week (Mon == 0).</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'fold=1'</span></code> means second pass in case of time jumping back for one hour.</strong></li>
</ul>
<h3 id="now">Now</h3>
<pre><code class="python language-python hljs"><D/DTn> = D/DT.today() <span class="hljs-comment"># Current local date or naive datetime.</span>
<DTn> = DT.utcnow() <span class="hljs-comment"># Naive datetime from current UTC time.</span>
<DTa> = DT.now(<tz>) <span class="hljs-comment"># Aware datetime from current tz time.</span>
</code></pre>
<h3 id="timezone">Timezone</h3>
<pre><code class="python language-python hljs"><tz> = UTC <span class="hljs-comment"># UTC timezone. London without DST.</span>
<tz> = tzlocal() <span class="hljs-comment"># Local timezone.</span>
<tz> = gettz(<span class="hljs-string">'<Cont.>/<City>'</span>) <span class="hljs-comment"># Timezone from 'Continent/City_Name' str.</span>
</code></pre>
<pre><code class="python language-python apache hljs"><DTa> = <DT>.astimezone(<tz>) <span class="hljs-comment"># Datetime, converted to passed timezone.</span>
<Ta/DTa> = <T/DT>.replace(tzinfo=<tz>) <span class="hljs-comment"># Unconverted object with new timezone.</span>
</code></pre>
<h3 id="encode">Encode</h3>
<pre><code class="python language-python apache hljs"><D/T/DT> = D/T/DT.fromisoformat(<span class="hljs-string">'<iso>'</span>) <span class="hljs-comment"># Object from ISO string.</span>
<DT> = DT.strptime(<str>, <span class="hljs-string">'<format>'</span>) <span class="hljs-comment"># Datetime from str, according to format.</span>
<D/DTn> = D/DT.fromordinal(<int>) <span class="hljs-comment"># D/DTn from days since Christ.</span>
<DTa> = DT.fromtimestamp(<real>, <tz>) <span class="hljs-comment"># DTa from seconds since Epoch in tz time.</span>
</code></pre>
<ul>
<li><strong>ISO strings come in following forms: <code class="python hljs"><span class="hljs-string">'YYYY-MM-DD'</span></code>, <code class="python hljs"><span class="hljs-string">'HH:MM:SS.ffffff[±<offset>]'</span></code>, or both separated by <code class="python hljs"><span class="hljs-string">'T'</span></code>. Offset is formatted as: <code class="python hljs"><span class="hljs-string">'HH:MM'</span></code>.</strong></li>
<li><strong>On Unix systems Epoch is <code class="python hljs"><span class="hljs-string">'1970-01-01 00:00 UTC'</span></code>, <code class="python hljs"><span class="hljs-string">'1970-01-01 01:00 CET'</span></code>, …</strong></li>
</ul>
<h3 id="decode">Decode</h3>
<pre><code class="python language-python apache hljs"><str> = <D/T/DT>.isoformat() <span class="hljs-comment"># ISO string representation.</span>
<str> = <D/T/DT>.strftime(<span class="hljs-string">'<format>'</span>) <span class="hljs-comment"># Custom string representation.</span>
<int> = <D/DT>.toordinal() <span class="hljs-comment"># Days since Christ, ignoring time and tz.</span>
<float> = <DT>.timestamp() <span class="hljs-comment"># Seconds since Epoch in local time or tz.</span>
</code></pre>
<h3 id="format-1">Format</h3>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">from</span> datetime <span class="hljs-keyword">import</span> datetime
<span class="hljs-meta">>>> </span>dt = datetime.strptime(<span class="hljs-string">'2015-05-14 23:39:00.00 +0200'</span>, <span class="hljs-string">'%Y-%m-%d %H:%M:%S.%f %z'</span>)
<span class="hljs-meta">>>> </span>dt.strftime(<span class="hljs-string">"%A, %dth of %B '%y, %I:%M%p %Z"</span>)
<span class="hljs-string">"Thursday, 14th of May '15, 11:39PM UTC+02:00"</span>
</code></pre>
<h4 id="restofthecodes">Rest of the codes:</h4>
<ul>
<li><strong><code class="python hljs"><span class="hljs-string">'a'</span></code> - Weekday, abbreviated name.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'b'</span></code> - Month, abbreviated name.</strong></li>
</ul>
<h2 id="arguments"><a href="#arguments" name="arguments">#</a>Arguments</h2>
<h3 id="insidefunctioncall">Inside Function Call</h3>
<pre><code class="python language-python hljs"><function>(<positional_args>) <span class="hljs-comment"># f(0, 0)</span>
<function>(<keyword_args>) <span class="hljs-comment"># f(x=0, y=0)</span>
<function>(<positional_args>, <keyword_args>) <span class="hljs-comment"># f(0, y=0)</span>
</code></pre>
<h3 id="insidefunctiondefinition">Inside Function Definition</h3>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(<nondefault_args>)</span>:</span> <span class="hljs-comment"># def f(x, y)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(<default_args>)</span>:</span> <span class="hljs-comment"># def f(x=0, y=0)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(<nondefault_args>, <default_args>)</span>:</span> <span class="hljs-comment"># def f(x, y=0)</span>
</code></pre>
<h2 id="splatoperator"><a href="#splatoperator" name="splatoperator">#</a>Splat Operator</h2>
<h3 id="insidefunctioncall-1">Inside Function Call</h3>
<p><strong>Splat expands a collection into positional arguments, while splatty-splat expands a dictionary into keyword arguments.</strong></p>
<pre><code class="python language-python hljs">args = (<span class="hljs-number">1</span>, <span class="hljs-number">2</span>)
kwargs = {<span class="hljs-string">'x'</span>: <span class="hljs-number">3</span>, <span class="hljs-string">'y'</span>: <span class="hljs-number">4</span>, <span class="hljs-string">'z'</span>: <span class="hljs-number">5</span>}
func(*args, **kwargs)
</code></pre>
<h4 id="isthesameas">Is the same as:</h4>
<pre><code class="python language-python hljs">func(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, x=<span class="hljs-number">3</span>, y=<span class="hljs-number">4</span>, z=<span class="hljs-number">5</span>)
</code></pre>
<h3 id="insidefunctiondefinition-1">Inside Function Definition</h3>
<p><strong>Splat combines zero or more positional arguments into a tuple, while splatty-splat combines zero or more keyword arguments into a dictionary.</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(*a)</span>:</span>
<span class="hljs-keyword">return</span> sum(a)
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>add(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
<span class="hljs-number">6</span>
</code></pre>
<h4 id="legalargumentcombinations">Legal argument combinations:</h4>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args)</span>:</span> <span class="hljs-comment"># f(1, 2, 3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *args)</span>:</span> <span class="hljs-comment"># f(1, 2, 3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args, z)</span>:</span> <span class="hljs-comment"># f(1, 2, z=3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *args, z)</span>:</span> <span class="hljs-comment"># f(1, 2, z=3)</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(**kwargs)</span>:</span> <span class="hljs-comment"># f(x=1, y=2, z=3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, **kwargs)</span>:</span> <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3)</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args, **kwargs)</span>:</span> <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *args, **kwargs)</span>:</span> <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args, y, **kwargs)</span>:</span> <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *args, z, **kwargs)</span>:</span> <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3)</span>
</code></pre>
<h3 id="otheruses">Other Uses</h3>
<pre><code class="python language-python hljs"><list> = [*<collection> [, ...]]
<set> = {*<collection> [, ...]}
<tuple> = (*<collection>, [...])
<dict> = {**<dict> [, ...]}
</code></pre>
<pre><code class="python language-python hljs">head, *body, tail = <collection>
</code></pre>
<h2 id="inline"><a href="#inline" name="inline">#</a>Inline</h2>
<h3 id="lambda">Lambda</h3>
<pre><code class="python language-python hljs"><function> = <span class="hljs-keyword">lambda</span>: <return_value>
<function> = <span class="hljs-keyword">lambda</span> <argument_1>, <argument_2>: <return_value>
</code></pre>
<h3 id="comprehension">Comprehension</h3>
<pre><code class="python language-python hljs"><list> = [i+<span class="hljs-number">1</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)] <span class="hljs-comment"># [1, 2, ..., 10]</span>
<set> = {i <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>) <span class="hljs-keyword">if</span> i > <span class="hljs-number">5</span>} <span class="hljs-comment"># {6, 7, 8, 9}</span>
<iter> = (i+<span class="hljs-number">5</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)) <span class="hljs-comment"># (5, 6, ..., 14)</span>
<dict> = {i: i*<span class="hljs-number">2</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)} <span class="hljs-comment"># {0: 0, 1: 2, ..., 9: 18}</span>
</code></pre>
<pre><code class="python language-python hljs">out = [i+j <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>) <span class="hljs-keyword">for</span> j <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)]
</code></pre>
<h4 id="isthesameas-1">Is the same as:</h4>
<pre><code class="python language-python hljs">out = []
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>):
<span class="hljs-keyword">for</span> j <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>):
out.append(i+j)
</code></pre>
<h3 id="mapfilterreduce">Map, Filter, Reduce</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> reduce
<iter> = map(<span class="hljs-keyword">lambda</span> x: x + <span class="hljs-number">1</span>, range(<span class="hljs-number">10</span>)) <span class="hljs-comment"># (1, 2, ..., 10)</span>
<iter> = filter(<span class="hljs-keyword">lambda</span> x: x > <span class="hljs-number">5</span>, range(<span class="hljs-number">10</span>)) <span class="hljs-comment"># (6, 7, 8, 9)</span>
<int> = reduce(<span class="hljs-keyword">lambda</span> out, x: out + x, range(<span class="hljs-number">10</span>)) <span class="hljs-comment"># 45</span>
</code></pre>
<h3 id="anyall">Any, All</h3>
<pre><code class="python language-python hljs"><bool> = any(<collection>) <span class="hljs-comment"># False if empty.</span>
<bool> = all(el[<span class="hljs-number">1</span>] <span class="hljs-keyword">for</span> el <span class="hljs-keyword">in</span> <collection>) <span class="hljs-comment"># True if empty.</span>
</code></pre>
<h3 id="ifelse">If - Else</h3>
<pre><code class="python language-python hljs"><expression_if_true> <span class="hljs-keyword">if</span> <condition> <span class="hljs-keyword">else</span> <expression_if_false>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>[a <span class="hljs-keyword">if</span> a <span class="hljs-keyword">else</span> <span class="hljs-string">'zero'</span> <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">0</span>, <span class="hljs-number">3</span>)]
[<span class="hljs-string">'zero'</span>, <span class="hljs-number">1</span>, <span class="hljs-string">'zero'</span>, <span class="hljs-number">3</span>]
</code></pre>
<h3 id="namedtupleenumclass">Namedtuple, Enum, Class</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
Point = namedtuple(<span class="hljs-string">'Point'</span>, <span class="hljs-string">'x y'</span>)
point = Point(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>)
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> enum <span class="hljs-keyword">import</span> Enum
Direction = Enum(<span class="hljs-string">'Direction'</span>, <span class="hljs-string">'n e s w'</span>)
Cutlery = Enum(<span class="hljs-string">'Cutlery'</span>, {<span class="hljs-string">'fork'</span>: <span class="hljs-number">1</span>, <span class="hljs-string">'knife'</span>: <span class="hljs-number">2</span>, <span class="hljs-string">'spoon'</span>: <span class="hljs-number">3</span>})
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-comment"># Warning: Objects will share the objects that are initialized in the dictionary!</span>
Creature = type(<span class="hljs-string">'Creature'</span>, (), {<span class="hljs-string">'p'</span>: Point(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>), <span class="hljs-string">'d'</span>: Direction.n})
creature = Creature()
</code></pre>
<h2 id="closure"><a href="#closure" name="closure">#</a>Closure</h2>
<p><strong>We have a closure in Python when:</strong></p>
<ul>
<li><strong>A nested function references a value of its enclosing function and then</strong></li>
<li><strong>the enclosing function returns the nested function.</strong></li>
</ul>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_multiplier</span><span class="hljs-params">(a)</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(b)</span>:</span>
<span class="hljs-keyword">return</span> a * b
<span class="hljs-keyword">return</span> out
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>multiply_by_3 = get_multiplier(<span class="hljs-number">3</span>)
<span class="hljs-meta">>>> </span>multiply_by_3(<span class="hljs-number">10</span>)
<span class="hljs-number">30</span>
</code></pre>
<ul>
<li><strong>If multiple nested functions within enclosing function reference the same value, that value gets shared.</strong></li>
<li><strong>To dynamically access function's first free variable use <code class="python hljs"><span class="hljs-string">'<function>.__closure__[0].cell_contents'</span></code>.</strong></li>
</ul>
<h3 id="partial">Partial</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> partial
<function> = partial(<function> [, <arg_1>, <arg_2>, ...])
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">import</span> operator <span class="hljs-keyword">as</span> op
<span class="hljs-meta">>>> </span>multiply_by_3 = partial(op.mul, <span class="hljs-number">3</span>)
<span class="hljs-meta">>>> </span>multiply_by_3(<span class="hljs-number">10</span>)
<span class="hljs-number">30</span>
</code></pre>
<h3 id="nonlocal">Nonlocal</h3>
<p><strong>If variable is being assigned to anywhere in the scope, it is regarded as a local variable, unless it is declared as a 'global' or a 'nonlocal'.</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_counter</span><span class="hljs-params">()</span>:</span>
i = <span class="hljs-number">0</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">()</span>:</span>
<span class="hljs-keyword">nonlocal</span> i
i += <span class="hljs-number">1</span>
<span class="hljs-keyword">return</span> i
<span class="hljs-keyword">return</span> out
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>counter = get_counter()
<span class="hljs-meta">>>> </span>counter(), counter(), counter()
(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
</code></pre>
<h2 id="decorator"><a href="#decorator" name="decorator">#</a>Decorator</h2>
<p><strong>A decorator takes a function, adds some functionality and returns it.</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-meta">@decorator_name</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">function_that_gets_passed_to_decorator</span><span class="hljs-params">()</span>:</span>
...
</code></pre>
<h3 id="debuggerexample">Debugger Example</h3>
<p><strong>Decorator that prints function's name every time it gets called.</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> wraps
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">debug</span><span class="hljs-params">(func)</span>:</span>
<span class="hljs-meta"> @wraps(func)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(*args, **kwargs)</span>:</span>
print(func.__name__)
<span class="hljs-keyword">return</span> func(*args, **kwargs)
<span class="hljs-keyword">return</span> out
<span class="hljs-meta">@debug</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(x, y)</span>:</span>
<span class="hljs-keyword">return</span> x + y
</code></pre>
<ul>
<li><strong>Wraps is a helper decorator that copies metadata of function add() to function out().</strong></li>
<li><strong>Without it <code class="python hljs"><span class="hljs-string">'add.__name__'</span></code> would return <code class="python hljs"><span class="hljs-string">'out'</span></code>.</strong></li>
</ul>
<h3 id="lrucache">LRU Cache</h3>
<p><strong>Decorator that caches function's return values. All function's arguments must be hashable.</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> lru_cache
<span class="hljs-meta">@lru_cache(maxsize=None)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">fib</span><span class="hljs-params">(n)</span>:</span>
<span class="hljs-keyword">return</span> n <span class="hljs-keyword">if</span> n < <span class="hljs-number">2</span> <span class="hljs-keyword">else</span> fib(n<span class="hljs-number">-2</span>) + fib(n<span class="hljs-number">-1</span>)
</code></pre>
<ul>
<li><strong>Recursion depth is limited to 1000 by default. To increase it use <code class="python hljs"><span class="hljs-string">'sys.setrecursionlimit(<depth>)'</span></code>.</strong></li>
</ul>
<h3 id="parametrizeddecorator">Parametrized Decorator</h3>
<p><strong>A decorator that accepts arguments and returns a normal decorator that accepts a function.</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> wraps
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">debug</span><span class="hljs-params">(print_result=False)</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">decorator</span><span class="hljs-params">(func)</span>:</span>
<span class="hljs-meta"> @wraps(func)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(*args, **kwargs)</span>:</span>
result = func(*args, **kwargs)
print(func.__name__, result <span class="hljs-keyword">if</span> print_result <span class="hljs-keyword">else</span> <span class="hljs-string">''</span>)
<span class="hljs-keyword">return</span> result
<span class="hljs-keyword">return</span> out
<span class="hljs-keyword">return</span> decorator
<span class="hljs-meta">@debug(print_result=True)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(x, y)</span>:</span>
<span class="hljs-keyword">return</span> x + y
</code></pre>
<h2 id="class"><a href="#class" name="class">#</a>Class</h2>
<pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <<span class="hljs-title">name</span>>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
self.a = a
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__repr__</span><span class="hljs-params">(self)</span>:</span>
class_name = self.__class__.__name__
<span class="hljs-keyword">return</span> <span class="hljs-string">f'<span class="hljs-subst">{class_name}</span>(<span class="hljs-subst">{self.a!r}</span>)'</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__str__</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> str(self.a)
<span class="hljs-meta"> @classmethod</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_class_name</span><span class="hljs-params">(cls)</span>:</span>
<span class="hljs-keyword">return</span> cls.__name__
</code></pre>
<h3 id="constructoroverloading">Constructor Overloading</h3>
<pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <<span class="hljs-title">name</span>>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a=None)</span>:</span>
self.a = a
</code></pre>
<h3 id="inheritance">Inheritance</h3>
<pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name, age)</span>:</span>
self.name = name
self.age = age
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Employee</span><span class="hljs-params">(Person)</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name, age, staff_num)</span>:</span>
super().__init__(name, age)
self.staff_num = staff_num
</code></pre>
<h3 id="multipleinheritance">Multiple Inheritance</h3>
<pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">A</span>:</span> <span class="hljs-keyword">pass</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">B</span>:</span> <span class="hljs-keyword">pass</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">C</span><span class="hljs-params">(A, B)</span>:</span> <span class="hljs-keyword">pass</span>
</code></pre>
<p><strong>MRO determines the order in which parent classes are traversed when searching for a method:</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>C.mro()
[<<span class="hljs-class"><span class="hljs-title">class</span> '<span class="hljs-title">C</span>'>, <<span class="hljs-title">class</span> '<span class="hljs-title">A</span>'>, <<span class="hljs-title">class</span> '<span class="hljs-title">B</span>'>, <<span class="hljs-title">class</span> '<span class="hljs-title">object</span>'>]</span></code>
</pre>
<h3 id="copy">Copy</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> copy <span class="hljs-keyword">import</span> copy, deepcopy
<object> = copy(<object>)
<object> = deepcopy(<object>)
</code></pre>
<h2 id="ducktypes"><a href="#ducktypes" name="ducktypes">#</a>Duck Types</h2>
<p><strong>A duck type is an implicit type that prescribes a set of special methods. Any object that has those methods defined is considered a member of that duck type.</strong></p>
<h3 id="comparable">Comparable</h3>
<ul>
<li><strong>If eq() method is not overridden, it returns <code class="python hljs"><span class="hljs-string">'id(self) == id(other)'</span></code>, which is the same as <code class="python hljs"><span class="hljs-string">'self is other'</span></code>.</strong></li>
<li><strong>That means all objects compare not equal by default.</strong></li>
</ul>
<pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyComparable</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
self.a = a
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__eq__</span><span class="hljs-params">(self, other)</span>:</span>
<span class="hljs-keyword">if</span> isinstance(other, type(self)):
<span class="hljs-keyword">return</span> self.a == other.a
<span class="hljs-keyword">return</span> <span class="hljs-keyword">False</span>
</code></pre>
<h3 id="hashable">Hashable</h3>
<ul>
<li><strong>Hashable object needs both hash() and eq() methods and its hash value should never change.</strong></li>
<li><strong>Hashable objects that compare equal must have the same hash value, meaning default hash() that returns <code class="python hljs"><span class="hljs-string">'id(self)'</span></code> will not do.</strong></li>
<li><strong>That is why Python automatically makes classes unhashable if you only implement eq().</strong></li>
</ul>
<pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyHashable</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
self.__a = copy.deepcopy(a)
<span class="hljs-meta"> @property</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">a</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> self.__a
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__eq__</span><span class="hljs-params">(self, other)</span>:</span>
<span class="hljs-keyword">if</span> isinstance(other, type(self)):
<span class="hljs-keyword">return</span> self.a == other.a
<span class="hljs-keyword">return</span> <span class="hljs-keyword">False</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__hash__</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> hash(self.a)
</code></pre>
<h3 id="collection">Collection</h3>
<ul>
<li><strong>Methods do not depend on each other, so they can be skipped if not needed.</strong></li>
<li><strong>Any object with defined getitem() is considered iterable, even if it lacks iter().</strong></li>
</ul>
<pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyCollection</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
self.a = a
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__len__</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> len(self.a)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__getitem__</span><span class="hljs-params">(self, i)</span>:</span>
<span class="hljs-keyword">return</span> self.a[i]
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__setitem__</span><span class="hljs-params">(self, i, value)</span>:</span>
self.a[i] = value
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__contains__</span><span class="hljs-params">(self, value)</span>:</span>
<span class="hljs-keyword">return</span> value <span class="hljs-keyword">in</span> self.a
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__iter__</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">for</span> el <span class="hljs-keyword">in</span> self.a:
<span class="hljs-keyword">yield</span> el
</code></pre>
<h3 id="callable">Callable</h3>
<pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Counter</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span>
self.i = <span class="hljs-number">0</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__call__</span><span class="hljs-params">(self)</span>:</span>
self.i += <span class="hljs-number">1</span>
<span class="hljs-keyword">return</span> self.i
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>counter = Counter()
<span class="hljs-meta">>>> </span>counter(), counter(), counter()
(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
</code></pre>
<h3 id="contextmanager">Context Manager</h3>
<pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyOpen</span><span class="hljs-params">()</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, filename)</span>:</span>
self.filename = filename
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__enter__</span><span class="hljs-params">(self)</span>:</span>
self.file = open(self.filename)
<span class="hljs-keyword">return</span> self.file
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__exit__</span><span class="hljs-params">(self, *args)</span>:</span>
self.file.close()
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">with</span> open(<span class="hljs-string">'test.txt'</span>, <span class="hljs-string">'w'</span>) <span class="hljs-keyword">as</span> file:
<span class="hljs-meta">... </span> file.write(<span class="hljs-string">'Hello World!'</span>)
<span class="hljs-meta">>>> </span><span class="hljs-keyword">with</span> MyOpen(<span class="hljs-string">'test.txt'</span>) <span class="hljs-keyword">as</span> file:
<span class="hljs-meta">... </span> print(file.read())
Hello World!
</code></pre>
<h2 id="enum"><a href="#enum" name="enum">#</a>Enum</h2>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> enum <span class="hljs-keyword">import</span> Enum, auto
<span class="hljs-class"><span class="hljs-keyword">class</span> <<span class="hljs-title">enum_name</span>><span class="hljs-params">(Enum)</span>:</span>
<member_name_1> = <value_1>
<member_name_2> = <value_2_a>, <value_2_b>
<member_name_3> = auto()
<span class="hljs-meta"> @classmethod</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_member_names</span><span class="hljs-params">(cls)</span>:</span>
<span class="hljs-keyword">return</span> [a.name <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> cls.__members__.values()]
</code></pre>
<pre><code class="python language-python hljs"><member> = <enum>.<member_name>
<member> = <enum>[<span class="hljs-string">'<member_name>'</span>]
<member> = <enum>(<value>)
name = <member>.name
value = <member>.value
</code></pre>
<pre><code class="python language-python hljs">list_of_members = list(<enum>)
member_names = [a.name <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> <enum>]
member_values = [a.value <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> <enum>]
random_member = random.choice(list(<enum>))
</code></pre>
<h3 id="inline-1">Inline</h3>
<pre><code class="python language-python hljs">Cutlery = Enum(<span class="hljs-string">'Cutlery'</span>, [<span class="hljs-string">'fork'</span>, <span class="hljs-string">'knife'</span>, <span class="hljs-string">'spoon'</span>])
Cutlery = Enum(<span class="hljs-string">'Cutlery'</span>, <span class="hljs-string">'fork knife spoon'</span>)
Cutlery = Enum(<span class="hljs-string">'Cutlery'</span>, {<span class="hljs-string">'fork'</span>: <span class="hljs-number">1</span>, <span class="hljs-string">'knife'</span>: <span class="hljs-number">2</span>, <span class="hljs-string">'spoon'</span>: <span class="hljs-number">3</span>})
</code></pre>
<h4 id="functionscannotbevaluessotheymustbewrapped">Functions can not be values, so they must be wrapped:</h4>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> partial
LogicOp = Enum(<span class="hljs-string">'LogicOp'</span>, {<span class="hljs-string">'AND'</span>: partial(<span class="hljs-keyword">lambda</span> l, r: l <span class="hljs-keyword">and</span> r),
<span class="hljs-string">'OR'</span> : partial(<span class="hljs-keyword">lambda</span> l, r: l <span class="hljs-keyword">or</span> r)})
</code></pre>
<h2 id="exceptions"><a href="#exceptions" name="exceptions">#</a>Exceptions</h2>
<pre><code class="python language-python hljs"><span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
<span class="hljs-keyword">try</span>:
x = int(input(<span class="hljs-string">'Please enter a number: '</span>))
<span class="hljs-keyword">except</span> ValueError:
print(<span class="hljs-string">'Oops! That was no valid number. Try again...'</span>)
<span class="hljs-keyword">else</span>:
print(<span class="hljs-string">'Thank you.'</span>)
<span class="hljs-keyword">break</span>
</code></pre>
<h3 id="raisingexception">Raising Exception</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">raise</span> ValueError(<span class="hljs-string">'A very specific message!'</span>)
</code></pre>
<h3 id="finally">Finally</h3>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">try</span>:
<span class="hljs-meta">... </span> <span class="hljs-keyword">raise</span> KeyboardInterrupt
<span class="hljs-meta">... </span><span class="hljs-keyword">finally</span>:
<span class="hljs-meta">... </span> print(<span class="hljs-string">'Goodbye, world!'</span>)
Goodbye, world!
Traceback (most recent call last):
File <span class="hljs-string">"<stdin>"</span>, line <span class="hljs-number">2</span>, <span class="hljs-keyword">in</span> <module>
KeyboardInterrupt
</code></pre>
<h2 id="print"><a href="#print" name="print">#</a>Print</h2>
<pre><code class="python language-python hljs">print(<el_1>, ..., sep=<span class="hljs-string">' '</span>, end=<span class="hljs-string">'\n'</span>, file=sys.stdout, flush=<span class="hljs-keyword">False</span>)
</code></pre>
<ul>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'file=sys.stderr'</span></code> for errors.</strong></li>
</ul>
<h3 id="prettyprint">Pretty Print</h3>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">from</span> pprint <span class="hljs-keyword">import</span> pprint
<span class="hljs-meta">>>> </span>pprint(dir())
[<span class="hljs-string">'__annotations__'</span>,
<span class="hljs-string">'__builtins__'</span>,
<span class="hljs-string">'__doc__'</span>, ...]
</code></pre>
<h2 id="input"><a href="#input" name="input">#</a>Input</h2>
<ul>
<li><strong>Reads a line from user input or pipe if present.</strong></li>
<li><strong>Trailing newline gets stripped.</strong></li>
<li><strong>Prompt string is printed to the standard output before reading input.</strong></li>
</ul>
<pre><code class="python language-python hljs"><str> = input(prompt=<span class="hljs-keyword">None</span>)
</code></pre>
<h4 id="printslinesuntileof">Prints lines until EOF:</h4>
<pre><code class="python language-python hljs"><span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
<span class="hljs-keyword">try</span>:
print(input())
<span class="hljs-keyword">except</span> EOFError:
<span class="hljs-keyword">break</span>
</code></pre>
<h2 id="commandlinearguments"><a href="#commandlinearguments" name="commandlinearguments">#</a>Command Line Arguments</h2>
<pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> sys
script_name = sys.argv[<span class="hljs-number">0</span>]
arguments = sys.argv[<span class="hljs-number">1</span>:]
</code></pre>
<h3 id="argparse">Argparse</h3>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> argparse <span class="hljs-keyword">import</span> ArgumentParser, FileType
p = ArgumentParser(description=<str>)
p.add_argument(<span class="hljs-string">'-<short_name>'</span>, <span class="hljs-string">'--<name>'</span>, action=<span class="hljs-string">'store_true'</span>) <span class="hljs-comment"># Flag</span>
p.add_argument(<span class="hljs-string">'-<short_name>'</span>, <span class="hljs-string">'--<name>'</span>, type=<type>) <span class="hljs-comment"># Option</span>
p.add_argument(<span class="hljs-string">'<name>'</span>, type=<type>, nargs=<span class="hljs-number">1</span>) <span class="hljs-comment"># Argument</span>
p.add_argument(<span class="hljs-string">'<name>'</span>, type=<type>, nargs=<span class="hljs-string">'+'</span>) <span class="hljs-comment"># Arguments</span>
args = p.parse_args()
value = args.<name>
</code></pre>
<ul>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'help=<str>'</span></code> for argument description.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'type=FileType(<mode>)'</span></code> for files.</strong></li>
</ul>
<h2 id="open"><a href="#open" name="open">#</a>Open</h2>
<p><strong>Opens a file and returns a corresponding file object.</strong></p>
<pre><code class="python language-python hljs"><file> = open(<span class="hljs-string">'<path>'</span>, mode=<span class="hljs-string">'r'</span>, encoding=<span class="hljs-keyword">None</span>)
</code></pre>
<h3 id="modes">Modes</h3>
<ul>
<li><strong><code class="python hljs"><span class="hljs-string">'r'</span></code> - Read (default).</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'w'</span></code> - Write (truncate).</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'x'</span></code> - Write or fail if the file already exists.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'a'</span></code> - Append.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'w+'</span></code> - Read and write (truncate).</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'r+'</span></code> - Read and write from the start.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'a+'</span></code> - Read and write from the end.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'t'</span></code> - Text mode (default).</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'b'</span></code> - Binary mode.</strong></li>
</ul>
<h3 id="file">File</h3>
<pre><code class="python language-python hljs"><file>.seek(<span class="hljs-number">0</span>) <span class="hljs-comment"># Moves to the start of the file.</span>
<file>.seek(offset) <span class="hljs-comment"># Moves 'offset' chars/bytes from the start.</span>
<file>.seek(offset, <anchor>) <span class="hljs-comment"># Anchor: 0 start, 1 current pos., 2 end.</span>
</code></pre>
<pre><code class="python language-python hljs"><str/bytes> = <file>.read(size=<span class="hljs-number">-1</span>) <span class="hljs-comment"># Reads 'size' chars/bytes or until EOF.</span>
<str/bytes> = <file>.readline() <span class="hljs-comment"># Returns a line.</span>
<list> = <file>.readlines() <span class="hljs-comment"># Returns a list of lines.</span>
<str/bytes> = next(<file>) <span class="hljs-comment"># Returns a line using buffer. Do not mix.</span>
</code></pre>
<pre><code class="python language-python hljs"><file>.write(<str/bytes>) <span class="hljs-comment"># Writes a string or bytes object.</span>
<file>.writelines(<list>) <span class="hljs-comment"># Writes a list of strings or bytes objects.</span>
<file>.flush() <span class="hljs-comment"># Flushes write buffer.</span>
</code></pre>
<ul>
<li><strong>Methods do not add or strip trailing newlines.</strong></li>
</ul>
<h3 id="readtextfromfile">Read Text from File</h3>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_file</span><span class="hljs-params">(filename)</span>:</span>
<span class="hljs-keyword">with</span> open(filename, encoding=<span class="hljs-string">'utf-8'</span>) <span class="hljs-keyword">as</span> file:
<span class="hljs-keyword">return</span> file.readlines()
</code></pre>
<h3 id="writetexttofile">Write Text to File</h3>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_file</span><span class="hljs-params">(filename, text)</span>:</span>
<span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'w'</span>, encoding=<span class="hljs-string">'utf-8'</span>) <span class="hljs-keyword">as</span> file:
file.write(text)
</code></pre>
<h2 id="path"><a href="#path" name="path">#</a>Path</h2>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> os <span class="hljs-keyword">import</span> path, listdir
<bool> = path.exists(<span class="hljs-string">'<path>'</span>)
<bool> = path.isfile(<span class="hljs-string">'<path>'</span>)
<bool> = path.isdir(<span class="hljs-string">'<path>'</span>)
<list> = listdir(<span class="hljs-string">'<path>'</span>)
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">from</span> glob <span class="hljs-keyword">import</span> glob
<span class="hljs-meta">>>> </span>glob(<span class="hljs-string">'../*.gif'</span>)
[<span class="hljs-string">'1.gif'</span>, <span class="hljs-string">'card.gif'</span>]
</code></pre>
<h3 id="pathlib">Pathlib</h3>