Lecture 6 Slides - Writing Functions

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Defining our Own Functions

CS 110

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def name_of_function(parameters):

statement(s)

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Keyword def marks the start of function header

A function name to uniquely identify it (snake case)

parameters (the way we pass data to a function)

colon (:) marks end of function header

function body has 1 or more statements, which have same indentation level (usually 4 spaces)

A function with inputs

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Dealing with inputs to functions

Positional parameters

  • Positional parameters are required
  • The order in which they are passed matters

Keyword parameters

  • Keyword parameters are always optional and are always specified by their keyword
  • They are always passed into a function after the positional parameters, but the order of keyword parameters doesn’t matter.
  • Keyword parameters always have a default value

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Need more practice writing functions?

Checkout the slides below and the example files for today!

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Say Hello! (Text example of Abstraction)

# Consider the following code:

print('Hello there, Obi-wan!')

print('How are you this morning?')

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Task 1 - Make this code into a function called say_hello so you can use it repeatedly.

Task 2 - Change the function so that it accepts a name as an input

Task 3 - Change the function so that the time of day is also an input.

Task 4 - Make the time of day input optional and have it default to morning

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Note: all of these are in the lecture files for today if you'd like to run them in IDLE

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# defining the function

def say_hello():

print('Hello there, Obi-wan!')

print('How are you this morning?')

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# calling (invoking) the function

say_hello()

say_hello()

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Function with no parameters

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Say Hello!

def say_hello():

print('Hello there, Obi-wan!')

print('How are you this morning?')

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Task 2 - Change the function so that it accepts a name as an input.

Task 3 - Change the function so that the time of day is also an input.

Task 4 - Make the time of day input optional and have it default to morning

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# defining the function

def say_hello(name):

print('Hello there,' + name + '!')

print('How are you this morning?')

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# calling (invoking) the function

say_hello('Varun')

say_hello('Grace')

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Function with 1 positional parameter

Arguments

Parameter (positional)

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Say Hello!

def say_hello(name):

print('Hello there,' + name + '!')

print('How are you this morning?')

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Task 3 - Change the function so that the time of day is also an input.

Task 4 - Make the time of day input optional and have it default to morning

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# defining the function

def say_hello(name, time_of_day):

print('Hello there,' + name + '!')

print('How are you this ' + time_of_day + '?')

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# calling (invoking) the function

say_hello('Varun', 'morning')

say_hello('Grace', 'evening')

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Function with 2 positional parameters

2 positional parameters

Arguments

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Say Hello!

def say_hello(name, time_of_day):

print('Hello there,' + name + '!')

print('How are you this ' + time_of_day + '?')

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Task 4 - Make the time of day input optional and have it default to morning

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# defining the function

def say_hello(name, time_of_day='morning'):

print('Hello there,' + name + '!')

print('How are you this ' + time_of_day + '?')

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# calling (invoking) the function

say_hello("Connor")

say_hello("Connor", time_of_day='evening')

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Function with 1 keyword parameter

keyword parameter

No keyword argument (uses default)

Keyword argument overrides default