Python Docstring


title: Docstring

Docstring

Docstring is a way for developers to communicate the purpose, parameters, requirements, and usage of a function in Python to other developers. It allows for ease of code maintenance and understanding.

Unlike conventional source code comments the docstring should describe what the
function does, not how.

A similar example to Docstring is @Javadoc in Java.

Docstring is written as a multi-line comment just after the declaration header in Python. There are 4 different parts to a docstring:

  1. Type of input, and type of output
    • Input/output can be obj, list, bool, int, str, float
  2. Description of function
    • Brief, but thorough description of what your function does
  3. Requirements
    • This is read by a human, so it does not have to be code
  4. Test cases (normally 2-3)

The general format is listed below.

Format of Docstring

def my_examplefunc(input_type1, input_type2): '''(input_type1, input_type2) -> output_type # Your first line will be the input/output. Remember the space around the arrow! Here is a description of my example function # Your second line will be the description REQ: type(input_type1) == list # Your next line (or lines) will be the requirements for the input of your function REQ: type(input_type2) == str >>> my_example_func([2, 3], "Hello World!") # After the requirements come test cases [2, 3] "Hello World" >>> my_example_func([7, 2], "Another test case") # Your first line of the test case is an example of the usage, prefaced by >>> [7, 2] "Another test case" # Your second line of the test case is the output >>> my_example_func([5, 6], "Last test case") [5, 6] "Last test case" ''' # Your code goes here, underneath the Docstring

Docstring is best understood with examples, so take a look at the below example program where the program outputs True if a number is less than 5, and False if a number is greater than 5.

Example 1

def is_less_than_five(some_number): '''(int) -> bool Returns True if the given number is less than 5, and False is the given number is greater than 5. REQ: some_number != 5 >>> is_less_than_five(4) True >>> is_less_than_five(6) False >>> is_less_than_five(100000) False ''' # Your code goes here

Some useful links:

Numpy and Google Docstrings are two commonly used approaches:

  • Google: http://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_google.html
  • Numpy: http://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_numpy.html
    Also, refer to some good old PEP commentary: https://www.python.org/dev/peps/pep-0257/

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