Python/conversions/octal_to_decimal.py

def oct_to_decimal(oct_string: str) -> int:
    """
    Convert a octal value to its decimal equivalent

    >>> oct_to_decimal("12")
    10
    >>> oct_to_decimal(" 12   ")
    10
    >>> oct_to_decimal("-45")
    -37
    >>> oct_to_decimal("2-0Fm")
    Traceback (most recent call last):
    ...
    ValueError: Non-octal value was passed to the function
    >>> oct_to_decimal("")
    Traceback (most recent call last):
    ...
    ValueError: Empty string was passed to the function
    >>> oct_to_decimal("19")
    Traceback (most recent call last):
    ...
    ValueError: Non-octal value was passed to the function
    """
    oct_string = str(oct_string).strip()
    if not oct_string:
        raise ValueError("Empty string was passed to the function")
    is_negative = oct_string[0] == "-"
    if is_negative:
        oct_string = oct_string[1:]
    if not oct_string.isdigit() or not all(0 <= int(char) <= 7 for char in oct_string):
        raise ValueError("Non-octal value was passed to the function")
    decimal_number = 0
    for char in oct_string:
        decimal_number = 8 * decimal_number + int(char)
    if is_negative:
        decimal_number = -decimal_number
    return decimal_number


if __name__ == "__main__":
    from doctest import testmod

    testmod()