python - Docstrings vs Comments

Question

I'm a bit confused over the difference between docstrings and comments in python.

In my class my teacher introduced something known as a 'design recipe', a set of steps that will supposedly help us students plot and organize our coding better in Python. From what I understand, the below is an example of the steps we follow - this so call design recipe (the stuff in the quotations):

def term_work_mark(a0_mark, a1_mark, a2_mark, ex_mark, midterm_mark):

    ''' (float, float, float, float, float) -> float

    Takes your marks on a0_mark, a1_mark, a2_mark, ex_mark and midterm_mark, 
    calculates their respective weight contributions and sums these 
    contributions to deliver your overall term mark out of a maximum of 55 (This
    is because the exam mark is not taken account of in this function)

    >>>term_work_mark(5, 5, 5, 5, 5)
    11.8
    >>>term_work_mark(0, 0, 0, 0, 0)
    0.0
    '''

    a0_component = contribution(a0_mark, a0_max_mark, a0_weight)
    a1_component = contribution(a1_mark, a1_max_mark, a1_weight)
    a2_component = contribution(a2_mark, a2_max_mark, a2_weight)
    ex_component = contribution(ex_mark, exercises_max_mark,exercises_weight)
    mid_component = contribution(midterm_mark, midterm_max_mark, midterm_weight)
    return (a0_component + a1_component + a2_component + ex_component + 
            mid_component)

As far as I understand this is basically a docstring, and in our version of a docstring it must include three things: a description, examples of what your function should do if you enter it in the python shell, and a 'type contract', a section that shows you what types you enter and what types the function will return.

Now this is all good and done, but our assignments require us to also have comments which explain the nature of our functions, using the token '#' symbol.

So, my question is, haven't I already explained what my function will do in the description section of the docstring? What's the point of adding comments if I'll essentially be telling the reader the exact same thing?

question from:https://stackoverflow.com/questions/19074745/docstrings-vs-comments

Answer 1

It appears your teacher is a fan of How to Design Programs ;)

I'd tackle this as writing for two different audiences who won't always overlap.

First there are the docstrings; these are for people who are going to be using your code without needing or wanting to know how it works. Docstrings can be turned into actual documentation. Consider the official Python documentation - What's available in each library and how to use it, no implementation details (Unless they directly relate to use)

Secondly there are in-code comments; these are to explain what is going on to people (generally you!) who want to extend the code. These will not normally be turned into documentation as they are really about the code itself rather than usage. Now there are about as many opinions on what makes for good comments (or lack thereof) as there are programmers. My personal rules of thumb for adding comments are to explain:

• Parts of the code that are necessarily complex. (Optimisation comes to mind)
• Workarounds for code you don't have control over, that may otherwise appear illogical
• I'll admit to TODOs as well, though I try to keep that to a minimum
• Where I've made a choice of a simpler algorithm where a better performing (but more complex) option can go if performance in that section later becomes critical

Since you're coding in an academic setting, and it sounds like your lecturer is going for verbose, I'd say just roll with it. Use code comments to explain how you are doing what you say you are doing in the design recipe.