Functions#

Functions#

A function is a named procedure with a series of instructions that can be called in your program to execute those instructions.

To call a function, you use its name and use () after it to make it a call. For example, print is actually a function defined by Python, so a “print statement” is really just calling this print function.

print()  # Prints a blank line

As we saw earlier, we can pass parameters to this function call to give it inputs. For example, the print function takes parameters for the things to print.

print('Hello world!')

Functions defined by Python are commonly called built-in functions. Some examples of built-in functions we will use commonly in CSE 163 are:

  • print

  • range

  • Casting: int , float , bool , str

  • Math:

    • abs to find absolute value

    • max to find the max of a sequence of numbers

    • min to find the min of a sequence of numbers

    • sum to find the sum of a sequence of numbers

Many functions can also return a value from their computation. For example min returns the minimum value of its inputs. You can do some more complex operations by combining the inputs and outputs of various functions like in the snippet below:

x = min(4, 7)  # x will store 4 (the return value of this function)
y = max(5, x)  # y will store 5 (the return value of this function)

Define your own Functions#

In the following snippet, we show how to define a function called greetings .

def greetings():
    print('hola!')

Note that by putting nothing in the parentheses, we are saying it takes no parameters.

To call the function, you need to actually use a function call like we showed before!

def greetings():
    print('hola!')

greetings()

Defining Parameters or Returns#

If you want to define a function that takes parameters, you put variable names in between the () for each parameter you want the function to take. If you want the function to return a value, you use a return statement like the example below.

def mean(a, b):
    print('Calling mean with', a, b)
    return (a + b) / 2


mean(1, 2)  # Have to call it passing in two parameters!

Functions in Context#

Recall that we said our reading snippets normally don’t show the main-method pattern. We make an exception in the next snippet to show a full Python program.

Notice, we are having you define a function called main by saying def main(): ! The mean function only gets called when we are actually running the program and the main method calls it.

def mean(a, b):
    print('Calling mean with', a, b)
    return (a + b) / 2


def main():
    print('The mean of 1 and 2 is:')
    print(mean(1, 2))


# The weird main-method pattern syntax!
if __name__ == '__main__':
    main()