Functions

Functions package reusable behavior behind a name.

def normalize_username(value: str) -> str:
    return value.strip().lower()

user = normalize_username("  Student  ")
print(user)

Parameters and return values

Parameters are inputs. return sends a result back to the caller. A function that only prints is harder to test than one that returns a value.

def is_valid_port(port: int) -> bool:
    return 1 <= port <= 65535

Good function design

• Give the function one clear responsibility.
• Use descriptive names.
• Validate inputs at trust boundaries.
• Avoid hidden global state.
• Raise or return meaningful errors.
• Add a short docstring when behavior is not obvious.

Small functions make automation scripts easier to review and safer to modify.