Strings

Introduction

Python strings are immutable Unicode sequences. Rich method API: split, join, strip, replace, format, f-strings.

Understanding the topic

Core concepts to understand:

• Immutable — every 'edit' creates a new string.
• f-strings (3.6+) are the modern format.
• join over += in loops.
• str vs bytes — Unicode vs raw octets.

Syntax reference

Visual flow / code:

name = "Alice"
greeting = f"Hello, {name.upper()}!"

# Split / join
parts = "a,b,c".split(",")  # ['a','b','c']
joined = "-".join(parts)    # 'a-b-c'

# Strip & replace
"  hi  ".strip()
"hello".replace("l", "L")

# Multi-line + f-string with format spec
pi = 3.14159
print(f"pi = {pi:.2f}")

# Encode/decode
b = "café".encode("utf-8")
s = b.decode("utf-8")

Execution workflow

Real-world use

Use f-strings everywhere. Use str.join for building large strings — it's O(n), while += in a loop is O(n²).

Best practices

• Prefer f-strings (fastest, clearest).
• Use join for concatenating many parts.
• Always specify encoding for bytes ↔ str.

Common mistakes

• s += '...' in a loop builds quadratic-time garbage.

Hands-on exercise

Interview preparation — practice these questions:

• Why are strings immutable?
• f-string vs % vs format?
• str vs bytes?

Summary

In summary: Immutable Unicode. f-strings + join = idiomatic.