Python/conversions/hexadecimal_to_decimal.py

hex_table = {hex(i)[2:]: i for i in range(16)}  # Use [:2] to strip off the leading '0x'


def hex_to_decimal(hex_string: str) -> int:
    """
    Convert a hexadecimal value to its decimal equivalent
    #https://www.programiz.com/python-programming/methods/built-in/hex

    >>> hex_to_decimal("a")
    10
    >>> hex_to_decimal("12f")
    303
    >>> hex_to_decimal("   12f   ")
    303
    >>> hex_to_decimal("FfFf")
    65535
    >>> hex_to_decimal("-Ff")
    -255
    >>> hex_to_decimal("F-f")
    Traceback (most recent call last):
    ...
    ValueError: Non-hexadecimal value was passed to the function
    >>> hex_to_decimal("")
    Traceback (most recent call last):
    ...
    ValueError: Empty string was passed to the function
    >>> hex_to_decimal("12m")
    Traceback (most recent call last):
    ...
    ValueError: Non-hexadecimal value was passed to the function
    """
    hex_string = hex_string.strip().lower()
    if not hex_string:
        raise ValueError("Empty string was passed to the function")
    is_negative = hex_string[0] == "-"
    if is_negative:
        hex_string = hex_string[1:]
    if not all(char in hex_table for char in hex_string):
        raise ValueError("Non-hexadecimal value was passed to the function")
    decimal_number = 0
    for char in hex_string:
        decimal_number = 16 * decimal_number + hex_table[char]
    return -decimal_number if is_negative else decimal_number


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

    testmod()