Basics

Comments

Comments in Python start with a #. There isn't a "true" mutli-line comment like /**/ in JavaScript.

# This is a comment
# You need multi-line comments?
# Start each line with hash

haiku

Primitive Data Types

Python has four primitive data types

• String

• Integer

• Float

• Boolean

type('spam, spam, and spam')
type(3)
type(3.14)
type(True)
type(False)

isinstance('spam, spam, and spam', str)
isinstance(3, int)
isinstance(3.14, float)
isinstance(True, bool)

Everything is an object in Python

isinstance('spam, spam, and spam', object)
isinstance(3, object)
isinstance(3.14, object)
isinstance(True, object)

Variables

To define a variable in Python, type

eggs_ive_eaten = 3
print(eggs_ive_eaten)

In Python, variable names:

• must start with a letter or underscore

• cannot start with a number

• contains only alpha-numeric characters and underscors

• are case-sensitive

NOTE: The convention for multi-word variable names in Python is snake_case

Variables can be reassigned

eggs_ive_eaten = 4
print(eggs_ive_eaten)

Unlike JavaScript, you cannot declare a variable without initialising it with a value. The closest equivalent would be assigning None

let spam
console.log(spam) // -> undefined

spam = None
print(spam) # -> None

String Operators

+	Concatenation
*	Replication

print('spam, ' * 3 + 'and eggs')

Arithmetic Operators

+	Addition
-	Subtraction
*	Multiplication
/	Division
//	Integer Division
%	Modulus
**	Exponent

print(4 + 2 * 3)   # -> 10
print((4 + 2) * 3) # -> 18

print(7 / 3)       # -> 2.3333333333333335
print(7 // 3)      # -> 2

print(4 ** 3)      # -> 64

Compound Assignment Operators

		equivalent to
+=	eggs += 2	eggs = eggs + 2
-=	eggs -= 2	eggs = eggs - 2
*=	eggs *= 2	eggs = eggs * 2
/=	eggs /= 2	eggs = eggs / 2
//=	eggs //= 3	eggs = eggs // 2
%=	eggs %= 2	eggs = eggs % 2
**=	eggs **= 2	eggs = eggs ** 2

Relational/Comparison Operators

==	Equal to
!=	Not equal to
<	Less than
>	Greater than
<=	Less than or equal to
>=	Greater than or equal to

print(42 == 42)         # -> True
print(42 == 42.0)       # -> False
print('spam' == 'Spam') # -> False
print('spam' != 'Spam') # -> True
print(42 == '42')       # -> False

In Python, you can "chain" conditions

n = 3
print(1 < n < 5) # -> True

Logical Operators

and

or

not

n = '3'
print(1 < n < 5)                      # -> TypeError
print(type(n) == 'int' and 1 < n < 5) # -> False