Python String Concatenation: +, join, and f-strings

Three Options

a, b = "hello", "world"

# 1. +
greeting = a + " " + b

# 2. f-string
greeting = f"{a} {b}"

# 3. join
greeting = " ".join([a, b])

Which to Use When

• f-strings — most readable. Use by default.
• join — combining many items from a list.
• + — fine for two or three short strings.

Why NOT to Use + in a Loop

# Slow: O(n²) behaviour
result = ""
for word in words:
    result += word

# Fast: O(n)
result = "".join(words)

Repeating a String

"-" * 20   # '--------------------'