Review

• Lists - appending, indexing
• Conditions - if, elif, else
• Loops - while, for

What we will cover this morning

• Functions
• Method calls
• (Even) More Data Types
• Python builtin functions

Functions

A named section of code that performs a specific task

This is also referred to as calling a function

a = '3'
print type(a)
a = float(a)
            

Function calls

a = 3
print type(a)
            

A function can take arguments

In the example above, the variable a is passed
as an argument to the function type

Arguments can also be called parameters

# Some more function call examples

int('32')
str(32)
            

Creating a Function

The following example is a function definition.
This allows us to create our own functions

def print_plus_5(x):
    print x + 5
            

The function definition has the following parts

• The def keyword signifies we are defining a function
• The name of the function being defined - print_plus_5
• The arguments in parentheses - x
• The function body, which is a block of indented code that executes when the function is called. - print x + 5

What to name your arguments

Similar to for loops, you decide how to refer to your arguments

def print_plus_5(duck):
    print duck + 5
            

Function returns

A function can also return a value

# function without return
def plus_5(x):
    x + 5

y = plus_5(4)
print y

#function with return
def return_plus_5(x):
    return x + 5

y = return_plus_5(4)
print y
            

Functions with no arguments

A function does not have to take arguments,
as in the following example:

def grass():
    print 'The grass is green.'

grass()
            

This is useful when the function does some work but doesn't need any parameters.
i.e. The function is intended to always do the same thing

Functions with more than one argument

A function can also take more than one argument separated by commas. For example:

def personal_info(name, age):
    return "My name is " + name + " and I am " + str(age) + " years old."

my_information = personal_info("Amy", 26)
print my_information
            

Let's Develop It

Pick one of the following exercises

• Write a function that a bar could use to check to see if a customer is of drinking age.

  isOfDrinkingAge(age)

• If it is a saturday in spring and it is above 65 degrees, Kermit plants flowers. Write a function to check whether he will plant flowers today.

  willKermitPlantFlowers(dayOfWeek, season, currentTemperature)

• Zach knows something is wrong with his basement if the temperature is below 50 or the humidity is above 70%. Write a function that can check whether his basement has a problem.

  basementIsOk(temperature, humidity)

Function Composition

Functions can also call other functions.

You can do this to break up tasks into small pieces and make your code easier to follow.

Function composition is when the output of one function acts as the input of another

def get_name():
    return raw_input("What is your name?")

def get_email_address():
    return raw_input("What is your address?")

def register():
    print "Please fill out the following information to register:"
    name = get_name()
    email = get_email_address()
    print name, "is registered under the email address", email
            

Method Calls

Methods are also called by name but are associated with a data type.

We have already called methods for strings and integers

a = 4
name = 'caleb'
sentence = 'the quick brown fox did the thing with the thing'
a_list = [1, 2, 3]

print name.capitalize()
print sentence.count('the')

a_list.append(4)
print a_list
            

Data Type: Dictionaries

A dictionary is a data type of key/value pairs, defined with {}

menu_categories = {
    'food': 'stuff you eat',
    'beverage': 'stuff you drink',
}
            

Think of words in a dictionary. The words are keys and the definitions are values.

Indexing on Dictionaries

Dictionaries aren't literally just for definitions. They represent a group of mappings. A mapping might be: menu items -> costs.

We can also index on dictionaries, but using the key instead of integers like in a list

menu = {
    'tofu': 4,
}

tofu_cost = menu['tofu']
            

Indexing on a key that doesn't exist results in a KeyError

Dictionary Methods

Some of the most essential methods are keys, values and items

menu = {
    'tofu': 4,
    'pizza': 8,
    'baguette': 3,
}

print menu.keys()
print menu.values()
print menu.items()
print menu.get('pizza')
print menu.get('water')
print menu.get('juice', 5)
            

If you aren't certain a key is present, you can use the get method

get will return None if the key isn't present.

The in operator

The in operator is used to determine if
an element is in a given data type

color = [255, 255, 0]
if 0 in color:
    print '0 is in the color'

menu = {'tofu': 4}
print 'tofu' in menu
print 4 in menu
            

Builtins for data types

Python provides several functions that
help us work with these data types.

Examples of using Builtins

# Using len() - Determines length
print len([1, 2])
print len("Hello")

# range() - Quickly creates a list of integers
print range(5)
print range(5, 10)
print range(0, 10, 2)

# sorted() - Sort a given list
grades = [93, 100, 60]
grades = sorted(grades)
print grades
            

String Formatting Operators

print 'To Do:'
to_dos = ['work', 'sleep', 'work']
for item in to_dos:
    print '%s' %(item)

name = 'Sally'
print 'Her name is {}'.format(name)
            

Function Practice

Write a function to...

# ...add 10 to any number
# ...divide any number by 100
# ...add any 2 numbers
# ...subtract any 2 numbers
# ...convert celsius to farenheight
# ...convert farenheight to celsius
# ...convert inches to centimeters
# ...convert centimeters to inches
# ...calculate sales tax for any given total amount
# ...calculate the area of a triangle (1/2 base * height)
# ...calculate the volume of a rectangular prism (length * width * height)
          

Questions?