WhatsNewInPython36.md

What's New In Python 3.6

https://docs.python.org/3/whatsnew/3.6.html

New Features

• PEP 498: Formatted string literals
• PEP 526: Syntax for variable annotations
• PEP 515: Underscores in Numeric Literals
• PEP 525: Asynchronous Generators
• PEP 530: Asynchronous Comprehensions
• PEP 487: Simpler customization of class creation
• PEP 487: Descriptor Protocol Enhancements
• PEP 519: Adding a file system path protocol
• PEP 495: Local Time Disambiguation
• PEP 529: Change Windows filesystem encoding to UTF-8
• PEP 528: Change Windows console encoding to UTF-8
• PEP 520: Preserving Class Attribute Definition Order
• PEP 468: Preserving Keyword Argument Order
• PEP 523: Adding a frame evaluation API to CPython

Other Language Changes

• A global or nonlocal statement must now textually appear before the first use of the affected name in the same scope. Previously this was a SyntaxWarning.
• It is now possible to set a special method to None to indicate that the corresponding operation is not available. For example, if a class sets __iter__() to None, the class is not iterable.
• Long sequences of repeated traceback lines are now abbreviated as "[Previous line repeated {count} more times]" (see traceback for an example).
• Import now raises the new exception ModuleNotFoundError (subclass of ImportError) when it cannot find a module. Code that currently checks for ImportError (in try-except) will still work.
• Class methods relying on zero-argument super() will now work correctly when called from metaclass methods during class creation.

New Modules

• secrets

Improved Modules

• array
• ast
• asyncio
• binascii
• cmath
• collections
• concurrent.futures
• contextlib
• datetime
• decimal
• distutils
• email
• encodings
• enum
• faulthandler
• fileinput
• hashlib
• http.client
• idlelib and IDLE
• importlib
• inspect
• json
• logging
• math
• multiprocessing
• operator
• os
• pathlib
• pdb
• pickle
• pickletools
• pydoc
• random
• re
• readline
• rlcompleter
• shlex
• site
• sqlite3
• socket
• socketserver
• ssl
• statistics
• struct
• subprocess
• sys
• telnetlib
• time
• timeit
• tkinter
• traceback
• tracemalloc
• typing
• unicodedata
• unittest.mock
• urllib.requests
• urllib.robotparser
• venv
• warnings
• winreg
• winsound
• xmlrpc.client
• zipfile
• zlib

Other Improvements

• When --version (short form: -V) is supplied twice, Python prints sys.version for detailed information.

Deprecated

New Keywords

• async and await are not recommended to be used as variable, class, function or module names. Introduced by PEP 492 in Python 3.5, they will become proper keywords in Python 3.7. Starting in Python 3.6, the use of async or await as names will generate a DeprecationWarning.

Deprecated Python Behavior

• Raising the StopIteration exception inside a generator will now generate a DeprecationWarning and will trigger a RuntimeError in Python 3.7. See PEP 479: Change StopIteration handling inside generators for details.
• The __aiter__() method is now expected to return an asynchronous iterator directly instead of returning an awaitable as previously. Doing the former will trigger a DeprecationWarning. Backward compatibility will be removed in Python 3.7.
• A backslash-character pair that is not a valid escape sequence now generates a DeprecationWarning. Although this will eventually become a SyntaxError, that will not be for several Python releases.
• When performing a relative import, falling back on __name__ and __path__ from the calling module when __spec__ or __package__ are not defined now raises an ImportWarning.

Deprecated Python modules, functions and methods

• The asynchat has been deprecated in favor of asyncio.
• The asyncore has been deprecated in favor of asyncio.
• Unlike other dbm implementations, the dbm.dumb module creates databases with the 'rw' mode and allows modifying the database opened with the 'r' mode. This behavior is now deprecated and will be removed in 3.8.
• The undocumented extra_path argument to the Distribution constructor is now considered deprecated and will raise a warning if set. Support for this parameter will be removed in a future Python release. See bpo-27919 for details.
• The support of non-integer arguments in getgrgid() has been deprecated.
• The importlib.machinery.SourceFileLoader.load_module() and importlib.machinery.SourcelessFileLoader.load_module() methods are now deprecated. They were the only remaining implementations of importlib.abc.Loader.load_module() in importlib that had not been deprecated in previous versions of Python in favour of importlib.abc.Loader.exec_module().
• The importlib.machinery.WindowsRegistryFinder class is now deprecated. As of 3.6.0, it is still added to sys.meta_path by default (on Windows), but this may change in future releases.
• Undocumented support of general bytes-like objects as paths in os functions, compile() and similar functions is now deprecated.
• Support for inline flags (?letters) in the middle of the regular expression has been deprecated and will be removed in a future Python version. Flags at the start of a regular expression are still allowed.
• OpenSSL 0.9.8, 1.0.0 and 1.0.1 are deprecated and no longer supported. In the future the ssl module will require at least OpenSSL 1.0.2 or 1.1.0..
• SSL-related arguments like certfile, keyfile and check_hostname in ftplib, http.client, imaplib, poplib, and smtplib have been deprecated in favor of context.
• A couple of protocols and functions of the ssl module are now deprecated. Some features will no longer be available in future versions of OpenSSL. Other features are deprecated in favor of a different API.
• The tkinter.tix module is now deprecated. tkinter users should use tkinter.ttk instead.
• The pyvenv script has been deprecated in favour of python3 -m venv. This prevents confusion as to what Python interpreter pyvenv is connected to and thus what Python interpreter will be used by the virtual environment.

Removed

• Unknown escapes consisting of '\' and an ASCII letter in regular expressions will now cause an error. In replacement templates for re.sub() they are still allowed, but deprecated. The re.LOCALE flag can now only be used with binary patterns.
• inspect.getmoduleinfo() was removed (was deprecated since CPython 3.3). inspect.getmodulename() should be used for obtaining the module name for a given path.
• traceback.Ignore class and traceback.usage, traceback.modname, traceback.fullmodname, traceback.find_lines_from_code, traceback.find_lines, traceback.find_strings, traceback.find_executable_lines methods were removed from the traceback module. They were undocumented methods deprecated since Python 3.2 and equivalent functionality is available from private methods.
• The tk_menuBar() and tk_bindForTraversal() dummy methods in tkinter widget classes were removed (corresponding Tk commands were obsolete since Tk 4.0).
• The open() method of the zipfile.ZipFile class no longer supports the 'U' mode (was deprecated since Python 3.4). Use io.TextIOWrapper for reading compressed text files in universal newlines mode.
• The undocumented IN, CDROM, DLFCN, TYPES, CDIO, and STROPTS modules have been removed. They had been available in the platform specific Lib/plat-*/ directories, but were chronically out of date, inconsistently available across platforms, and unmaintained. The script that created these modules is still available in the source distribution at Tools/scripts/h2py.py.
• The deprecated asynchat.fifo class has been removed.