Functions & Comprehensions

Functions are reusable blocks. def, then params, return value:

def greet(name):
    return f"hi {name}"

greet("Alice")  # "hi Alice"

Defaults turn params optional. Pass by keyword to skip ahead:

def total(price, qty, tax_rate=0.08):
    subtotal = price * qty
    return subtotal + subtotal * tax_rate

total(10, 5)                  # uses default
total(10, 5, tax_rate=0.10)   # override

List comprehensions replace the for/append loop. These two do the same thing, but the second one is what experienced Python looks like:

squares = []
for x in range(5):
    squares.append(x ** 2)

squares = [x ** 2 for x in range(5)]

Add a condition to filter:

evens = [x for x in range(10) if x % 2 == 0]
passing = [s for s in scores if s >= 70]

Dict comprehensions work the same way:

grade_book = {name: score for name, score in zip(names, scores)}
doubled = {k: v * 2 for k, v in prices.items()}