Beginner's Python
Cheat Sheet
Variables and Strings
Variables are used to assign labels to values. A string is a
series of characters, surrounded by single or double quotes.
Python's f-strings allow you to use variables inside strings to
build dynamic messages.
Hello world
print("Hello world!")
Hello world with a variable
msg = "Hello world!"
print(msg)
f-strings (using variables in strings)
first_name = 'albert'
last_name = 'einstein'
full_name = f"{first_name} {last_name}"
print(full_name)
Lists
A list stores a series of items in a particular order. You
access items using an index, or within a loop.
Make a list
bikes = ['trek', 'redline', 'giant']
Get the rst item in a list
first_bike = bikes[0]
Get the last item in a list
last_bike = bikes[-1]
Looping through a list
for bike in bikes:
print(bike)
Adding items to a list
bikes = []
bikes.append('trek')
bikes.append('redline')
bikes.append('giant')
Making numerical lists
squares = []
for x in range(1, 11):
squares.append(x**2)
Lists (cont.)
List comprehensions
squares = [x**2 for x in range(1, 11)]
Slicing a list
finishers = ['sam', 'bob', 'ada', 'bea']
first_two = finishers[:2]
Copying a list
copy_of_bikes = bikes[:]
Tuples
Tuples are similar to lists, but the items in a tuple can't be
modied.
Making a tuple
dimensions = (1920, 1080)
resolutions = ('720p', '1080p', '4K')
If statements
If statements are used to test for particular conditions and
respond appropriately.
Conditional tests
equal x == 42
not equal x != 42
greater than x > 42
or equal to x >= 42
less than x < 42
or equal to x <= 42
Conditional tests with lists
'trek' in bikes
'surly' not in bikes
Assigning boolean values
game_active = True
can_edit = False
A simple if test
if age >= 18:
print("You can vote!")
If-elif-else statements
if age < 4:
ticket_price = 0
elif age < 18:
ticket_price = 10
elif age < 65:
ticket_price = 40
else:
ticket_price = 15
Dictionaries
Dictionaries store connections between pieces of
information. Each item in a dictionary is a key-value pair.
A simple dictionary
alien = {'color': 'green', 'points': 5}
Accessing a value
print(f"The alien's color is {alien['color']}.")
Adding a new key-value pair
alien['x_position'] = 0
Looping through all key-value pairs
fav_numbers = {'eric': 7, 'ever': 4, 'erin': 47}
for name, number in fav_numbers.items():
print(f"{name} loves {number}.")
Looping through all keys
fav_numbers = {'eric': 7, 'ever': 4, 'erin': 47}
for name in fav_numbers.keys():
print(f"{name} loves a number.")
Looping through all the values
fav_numbers = {'eric': 7, 'ever': 4, 'erin': 47}
for number in fav_numbers.values():
print(f"{number} is a favorite.")
User input
Your programs can prompt the user for input. All input is
stored as a string.
Prompting for a value
name = input("What's your name? ")
print(f"Hello, {name}!")
Prompting for numerical input
age = input("How old are you? ")
age = int(age)
pi = input("What's the value of pi? ")
pi = float(pi)
Python Crash Course
A Hands-on, Project-Based
Introduction to Programming
ehmatthes.github.io/pcc_3e
