Strings in Python (str type, immutability, overview)

Strings as a type in Python are immutable Unicode sequences—indexing, slicing, and methods return new objects. This lesson ties the big picture together: text is central to I/O, logs, JSON, and algorithms alike.

Why this shows up in the real world

HTTP bodies are bytes decoded to str for JSON and HTML. CLI programs spend most time moving strings between user, OS, and network.

Core idea (explained for students)

str supports rich methods (split, strip, startswith) and participates in formatting (f-strings). Interning of small literals is an implementation detail—never rely on is for equality.

Try this in Python

s = "hello"
print(type(s), s[1:4], "world" in "hello world")

Common mistakes

• Mutability assumptions from other languages.
• Treating bytes and str interchangeably without explicit encode/decode.

Key takeaways

• Think of strings as cheap to read, paid writes (new allocations).
• Standardize on UTF-8 at system boundaries.