Functions I

Use comments to add documentation to programs.

# This sentence isn't executed by Python.
adjustment = 0.5   # Neither is this - anything after '#' is ignored.

A function may take zero or more arguments.

  • We have seen some functions already — now let’s take a closer look.

  • An argument is a value passed into a function.

  • len takes exactly one.

  • int, str, and float create a new value from an existing one.

  • print takes zero or more.

  • print with no arguments prints a blank line.

    • Must always use parentheses, even if they’re empty, so that Python knows a function is being called.

print('before')
print()
print('after')

Every function returns something.

  • Every function call produces some result.

  • If the function doesn’t have a useful result to return, it usually returns the special value None. None is a Python object that stands in anytime there is no value.

result = print('example')
print('result of print is', result)

Commonly-used built-in functions include max, min, and round.

  • Use max to find the largest value of one or more values.

  • Use min to find the smallest.

  • Both work on character strings as well as numbers.

    • “Larger” and “smaller” use (0-9, A-Z, a-z) to compare letters.

print(max(1, 2, 3))
print(min('a', 'A', '0'))

Use the built-in function help to get help for a function.

  • Every built-in function has online documentation.

help(round)

The Jupyter Notebook has two ways to get help.

  • Option 1: Place the cursor near where the function is invoked in a cell (i.e., the function name or its parameters),

    • Hold down Shift, and press Tab.

    • Do this several times to expand the information returned.

  • Option 2: Type the function name in a cell with a question mark after it. Then run the cell.

Write your own functions in python

Exercise: Write the code in your notebook and replace the underscored lines to get the desired result

def max_of_two( __, __ ):
    if __ > __:
        return __
    return __

def max_of_three( __, __, z ):
    return max_of_two( x, max_of_two( __, __ ) )

print(max_of_three(3, 6, -5))

Exercise: Write the code in your notebook and replace the underscored lines to get the desired result

def sum(______):
    total = 0
    for number in numbers:
        total += number
    return total
print(sum((8, 2, 3, 0, 7)))