print() displays output

print("Hello, world!")

Shows: Hello, world! Each print() shows up on its own line.

Strings are text in quotes

"pizza"
"I love coding!"
"( ^_^ )"

Quotes always come in pairs: one to start, one to end.

input() asks a question

name = input("What is your name? ")
print("Hi " + name)

The program waits for the user to type and press Enter. Leave a space at the end of your question.

+ joins strings

print("My name is " + "Maya")

Shows: My name is Maya. Forget the space and you get “My name isMaya”.

A variable stores a value

name = "Maya"
print(name)

Variable name on the left, value on the right. Read = as “stores”.

Quotes change everything

name = "Maya"
print(name)      # Maya
print("name")    # name

No quotes: use what’s in the box. Quotes: print the exact text.

A new value replaces the old one

food = "pizza"
food = "tacos"
print(food)      # tacos

A variable holds one value at a time: the newest one.

Naming rules

• No spaces: use my_name
• Can’t start with a number
• Capitals matter: Name and name are different
• Pick names that describe the value

Math operators

print(5 + 3)    # 8   add
print(9 - 4)    # 5   subtract
print(6 * 7)    # 42  multiply
print(7 / 2)    # 3.5 divide

Multiply is a star *, not an x.

Same +, different jobs

print("5" + "5")  # 55
print(5 + 5)      # 10

Strings get glued together. Integers get added.

input() always gives a string

age = int(input("Age? "))
print(age + 1)

int() turns the typed text into a number so you can do math.

str() for sentences

print("You are " + str(age))

str() turns a number back into text so + can join it to a sentence.

A boolean is True or False

is_raining = True
has_homework = False

A new data type with only two values. No quotes, and always a capital T or F.

Comparisons give a boolean

print(5 > 3)          # True
print(10 == 2)        # False
print("cat" == "cat")  # True

Python checks the comparison and answers True or False.

Comparison operators

= stores a value. == asks “are these equal?”

if runs code when it’s True

answer = input("Like pizza? ")
if answer == "yes":
    print("Same!")

If the condition is True, the indented code runs. If it’s False, Python skips it.

else is the backup plan

if answer == "yes":
    print("Same!")
else:
    print("More for me!")

else runs when the if is False. One of the two always runs.

elif adds more choices

if score >= 90:
    print("Amazing!")
elif score >= 70:
    print("Nice job!")
else:
    print("Keep practicing!")

Python checks from top to bottom and runs only the first one that’s True.

The two rules

• End the if, elif or else line with a colon :
• Indent the code inside with 4 spaces (or the Tab key)
• Only indented lines belong to the if