String Concatenation (+, join, f-strings)

Concatenation glues pieces into one string—+, ''.join(iterable), or f-strings. For many fragments, join avoids repeated full-string copies that += in a loop creates.

Why this shows up in the real world

URL builders join scheme, host, path, and query segments. CSV rows join fields with commas while escaping special cells.

Core idea (explained for students)

Use sep.join(parts) when you have a list; use f-strings for a fixed template with values. Coerce non-strings with str(x) before joining.

Try this in Python

def build_path(*segments: str) -> str:
    return "/".join(s.strip("/") for s in segments if s)


print(build_path("api", "v1", "users"))

Common mistakes

• join on non-string elements raises—map to str first.
• Accidentally doubling separators when some parts already end with /.

Key takeaways

• Treat join as the default bulk concatenator in Python.
• For two pieces only, a + b is perfectly fine and readable.