Python in 5 Minutes

If you already know any programming language, you know most of Python.

Variables and expressions

No type declarations. No semicolons. Just assign and compute.

Python

x = 5
print(x + 3)
print(x * 2)

Functions

Define with def. Indentation marks the body. return sends a value back.

Python

def square(x):
    return x * x

print(square(5))
print(square(12))

Lists

Square brackets make a list. Index from zero. Slice with start:end. len() gives the length.

Python

nums = [1, 2, 3, 4, 5]
print(nums[0])      # first element
print(nums[1:3])    # slice: elements 1 and 2
print(len(nums))    # length

Conditionals

if, elif, else. Indentation replaces braces.

Python

def classify(n):
    if n < 0:
        return "negative"
    elif n == 0:
        return "zero"
    else:
        return "positive"

print(classify(-1))
print(classify(0))
print(classify(7))

List comprehensions

Build a new list by transforming and filtering an existing one, all in one line.

Python

squares = [x*x for x in range(5)]
print(squares)

evens = [x for x in range(10) if x % 2 == 0]
print(evens)

Lambda

lambda creates a small anonymous function. Combine with map() and filter() to transform sequences.

Python

square = lambda x: x * x
print(square(5))

print(list(map(lambda x: x * 2, [1, 2, 3])))
print(list(filter(lambda x: x > 2, [1, 2, 3, 4, 5])))

Dictionaries

Key-value pairs. Create with dict(), access by key, iterate over items.

Python

ages = dict(alice=30, bob=25, carol=35)
print(ages["alice"])

for name, age in ages.items():
    print(name, "is", age)

That's enough to read every page on this site.