Python Crash Course: A Hands-On, Project-Based Introduction to Programming

by Eric Matthes

Numerical Lists

range() Function

for value in range(1,5):

it doesn’t print the number 5:

from 1 to 5, you

use range(1,6):

numbers = list(range(1,6))

even_numbers = list(range(2,11,2))

code. A list comprehension allows you to generate this same list in just one line of code.

squares = [value**2 for value in range(1,11)]

To make a slice, you specify the index of the first and last elements you want to work with.

Python stops one item before the second index you specify.

players[0:3])

For example, if we want to output the last three players on the roster, we can use the slice players[-3:]:

list, you can make a slice that includes the entire original list by omitting the first index and the second index ([:]).

Tuples

Python refers to values that cannot change as immutable, and an immutable list is called a tuple.

A tuple looks just like a list except you use parentheses instead of square brackets.

➊ dimensions = (200, 50)

When compared with lists, tuples are simple data structures. Use them when you want to store a set of values that should not be changed throughout the life of a program.

about tuples, which provide a degree of protection to a set of values that shouldn’t change,

➊ if car == 'bmw':

already in a list, use the keyword in.

keyword not in this situation.

Indentation plays the same role in if statements as it did in for loops.

The if-elif-else Chain

elif age < 18:

allow you to connect pieces of related information.

nest dictionaries

alien_0 = {'color': 'green', 'points': 5} print(alien_0['color']) print(alien_0['points'])

A dictionary in Python is a collection of key-value pairs.

In Python, a dictionary is wrapped in braces, {},

A key-value pair is a set of values associated with each other.

can add new key-value pairs to a dictionary at any time.

➊ for key, value in user_0.items(): ➋ print("\nKey: " + key) ➌ print("Value: " + value)

Looping Through All the Keys in a Dictionary

Looping through the keys is actually the default

behavior

for name in favorite_languages:

for name in favorite_languages.keys():

The keys() method isn’t just for looping: It actually returns a list of all the keys,

Nesting

'aeinstein': { 'first': 'albert', 'last': 'einstein', 'location': 'princeton', },

message = input("Tell me something, and I will repeat it back to you: ")

name = input(prompt)

➊ def greet_user():

Default Values

The return statement takes a value

return person

When you pass a list to a function, the function can modify the list.