Question

Write a function to find average of a list of numbers. Your function should be able to handle an empty list and also list containing string.

Answer 1

The following function converts numeric strings such as "20" to numbers and ignores non-numeric values. It returns None when no valid numbers are present.

def average(values):
    numbers = []

    for value in values:
        try:
            numbers.append(float(value))
        except (TypeError, ValueError):
            # Ignore values that cannot be converted to numbers.
            continue

    if not numbers:
        return None

    return sum(numbers) / len(numbers)


print(average([10, 20, "30"]))       # 20.0
print(average([10, "hello", 20]))    # 15.0
print(average([]))                    # None

Returning None clearly indicates that an average cannot be calculated for an empty or completely invalid list.