Before you do anything else, make a fork of this repository by clicking the "Fork" button at the top right of this page. You will need to be logged in to a GitHub account (feel free to use either pair's account). Once you've made your fork, scroll back down and you should be able to continue reading this text where you left off.
Now, clone your fork (note: make sure not to clone the original, but your own fork!) to your local machine.
As you work through the exercises, each time you complete a function, make a commit. Use the --author flag or set the .gitconfig so that the commits show up under the right name!
First, work through the following resources on lists:
- http://learnpythonthehardway.org/book/ex32.html
- http://learnpythonthehardway.org/book/ex33.html
- http://learnpythonthehardway.org/book/ex34.html
- http://learnpythonthehardway.org/book/ex38.html
- http://learnpython.org/en/Lists
- http://docs.python.org/tutorial/introduction.html#lists
- http://docs.python.org/tutorial/datastructures.html#more-on-lists --> stop reading before section 5.1.1
http://learnpythonthehardway.org/book/ex47.html
In this exercise directory there are two files: list_operations.py and
test_list_operations.py.
list_operations.py contains lots of empty functions that take an input list and don't do anything.
test_list_operations.py contains lots of full functions that ... ? Well, let's find out.
####Try it out!
Try running python test_list_operations.py at the CLI prompt. You should see a lot of console output that ends with the following text:
----------------------------------------------------------------------
Ran 25 tests in 0.007s
FAILED (failures=25)
Wow, 25 failures. That doesn't sound good. What just happened?
Well, test_list_operations.py just ran 25 'tests' on list_operations.py and none of them worked. How did it do that?
####What's a test?
Each function in test_list_operations.py (which I will now refer to as a test) does four things:
- Gets some sample data (initialized in
setUp()and passed in to each function withself-- more on this on a later date) - Sends the sample data through a
list_operations.pyfunction (there's one test function for each regular function) - Defines what the correct output for each function should be based on the input
- Tests whether the result of the
list_operations.pyfunction matches the expected input ( it asserts equality )
If all of the asserted equality turns out true, then your test passes. If any of them fails, your test fails.
All of your tests failed because, obviously, there's nothing in any of your list_operation functions. So whatever your function returns (it returns nothing) doesn't match what the test expects (very specific things, including not nothing).
For example: test_1_A_head() checks the function head() in list_operations.py. It asserts that the result of calling the function head() with the test data months should result in 'Jan'.
One thing to note is that test_1_A_head() is laid out differently than a test like test_1_J_replace_head(). The latter calls the function first, then checks the result in a different step. This is important! Why?
When a test fails, it will print the un-matching-ness in the terminal. This may be helpful for troubleshooting your list operators. Also, sometimes you may see something like:
FAILED (failures=24, errors=1)
Don't get too excited that your failure number has gone down by one -- an error means that the function call errored out when the test called it. You'll be able to see the error message it returned if you scroll up in the terminal to that test's section.
Your mission is to get all the tests to pass by actually writing the functions in list_operations.py. When you've succeeded, you'll see only this output when you run your tests:
.........................
----------------------------------------------------------------------
Ran 25 tests in 0.002s
OK
The fundamental operations on lists in Python are those that are part of the language syntax and/or cannot be implemented in terms of other list operations:
- List literals (
[],['hello'],[3, 1, 4, 1, 5, 9], etc.) - List indexing (
some_list[index]) - List indexing assignment (
some_list[index] = value) - List slicing (
some_list[start:end]) - List slicing assignment (
some_list[start:end] = another_list) - List index deletion (
del some_list[index]) - List slicing deletion (
del some_list[start:end])
In this section you will implement functions that each use just one of the above
operations. The docstring of each function describes what it should do. Consult
test_list_operations.py for concrete examples of the expected function behavior.
- Remember to commit your code after you complete each function!
DO NOT USE ANY OF THE BUILT IN LIST METHODS
DO NOT USE len(l)
GET A CODE REVIEW BEFORE MOVING ON TO PART 2
Note: this means that you should call over one of the instructors/TA and run the tests for them, showing that the appropriate tests do pass, and then have them look over the actual code. Make sure you have committed all your code and pushed it to your fork before calling over an instructor/TA to review.
In this section you will implement your own versions of the standard list methods. You should use only the primitive operations from Part 1 and 2 in your implementations. For loops are also allowed, such as the following:
for element in some_list:
# Do something with element
Each custom method imitates a built-in list method, as described by the docstring for each function. Play with the built-in methods in the Python REPL to get a feel for how they work before trying to write your custom version. You may also look at the test_list_operations.py file for concrete examples of expected behavior.
Again, remember to commit your code as you go and don't forget to get a code review when you think you're finished!