How to Create a Function in Python: Parameters and return

Start with a small, explicit task

Write a pure conversion from nonnegative whole minutes to seconds. Check two inputs and reject a negative value. Then print one returned result outside the function. The example’s input contract is deliberately narrow; it does not attempt to infer units or parse arbitrary user text.

Run the complete example

This original example was checked with Python 3.12.14. Save it as python_create_function.py and run it with Python 3.12. It uses only the standard library. The assertions check the stated results.

def minutes_to_seconds(minutes):
    if minutes < 0:
        raise ValueError("minutes must be nonnegative")
    return minutes * 60
result = minutes_to_seconds(3)
assert result == 180
assert minutes_to_seconds(0) == 0
try:
    minutes_to_seconds(-1)
except ValueError:
    rejected = True
else:
    raise AssertionError("expected negative input rejection")
assert rejected
def show_seconds(seconds):
    print(f"{seconds} seconds")
printed_return = show_seconds(result)
assert printed_return is None
print("calculation returned:", result)

Explain the result

minutes is the parameter inside the function, while 3 is the argument supplied by the first call. return ends the calculation and makes 180 available to result. A second call works independently with zero. The negative call takes a deliberate exception path instead of producing an invalid conversion under the stated nonnegative rule.

show_seconds prints a label but reaches the end without an explicit return, so its return value is None. The displayed text and the returned value are different things. The conversion function can therefore be reused in a calculation or assertion without forcing console output on every caller.

Avoid these mistakes

Defining a function does not execute its body; call it with the required arguments. Keep indentation consistent so the return belongs to the function. This example assumes whole numeric minutes as stated; validate types or parse strings at the boundary when your actual caller has a wider input contract.