""" Convert Base 10 (Decimal) Values to Hexadecimal Representations """

# set decimal value for each hexadecimal digit
values = {
    0:'0',
    1:'1',
    2:'2',
    3:'3',
    4:'4',
    5:'5',
    6:'6',
    7:'7',
    8:'8',
    9:'9',
    10:'a',
    11:'b',
    12:'c',
    13:'d',
    14:'e',
    15:'f'
}

def decimal_to_hexadecimal(decimal):
    """
        take integer decimal value, return hexadecimal representation as str beginning with 0x
        >>> decimal_to_hexadecimal(5)
        '0x5'
        >>> decimal_to_hexadecimal(15)
        '0xf'
        >>> decimal_to_hexadecimal(37)
        '0x25'
        >>> decimal_to_hexadecimal(255)
        '0xff'
        >>> decimal_to_hexadecimal(4096)
        '0x1000'
        >>> decimal_to_hexadecimal(999098)
        '0xf3eba'
        >>> # negatives work too
        >>> decimal_to_hexadecimal(-256)
        '-0x100'
        >>> # floats are acceptable if equivalent to an int
        >>> decimal_to_hexadecimal(17.0)
        '0x11'
        >>> # other floats will error
        >>> decimal_to_hexadecimal(16.16) # doctest: +ELLIPSIS
        Traceback (most recent call last):
        ...
        AssertionError
        >>> # strings will error as well
        >>> decimal_to_hexadecimal('0xfffff') # doctest: +ELLIPSIS
        Traceback (most recent call last):
        ...
        AssertionError
        >>> # results are the same when compared to Python's default hex function
        >>> decimal_to_hexadecimal(-256) == hex(-256)
        True
    """
    assert type(decimal) in (int, float) and decimal == int(decimal)
    hexadecimal = ''
    negative = False
    if decimal < 0:
        negative = True
        decimal *= -1
    while decimal > 0:
        decimal, remainder = divmod(decimal, 16)
        hexadecimal = values[remainder] + hexadecimal
    hexadecimal = '0x' + hexadecimal
    if negative:
        hexadecimal = '-' + hexadecimal
    return hexadecimal

if __name__ == '__main__':
    import doctest
    doctest.testmod()