Functions

Python Style guide

The 3 steps of a function

1. input
2. transform
3. Output

you can do two things with functions

• Define it (a block of re-usable code => loop)
• call it

# define the function
def do_nothing(parameters):
        # since functions do something, use a verb as function name
    pass

# call the function
do_nothing()

Examples of functions

• len
• open
• reversed
• password_validator

Programming interface

• Function caller (client) only needs to know about the inputs and output
  • Implementation details are hidden, how it does the processing is hidden from us (Like a black box)
• Because we don’t know the implementation we can concentrate on higher level thingking - how modules work together, instead of how they work.

Calling Functions

• function name and parenthesis and values (arguments within the parenthesis)
• number of arguments depends on the function’s defintion

Function implementation

• is ideally self contained.
• we will only change this part of code should we need to fix bugs or come up with a better algorithm
• we use parameters as part of the processing
• Returns an output

Readability counts docstring vs comments [Zen of Python]

docstring describes the function’s external behavior, and the parameters it takes. comments should document internal info about how the code works.

• documentation to a function definition (page 152)

def echo(anything):
    'echo returns its input argument'
    return anything

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