''' Purpose: better experience functional development

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'''
import math

def donut( d, h ) :
    ''' Returns the volume of donut whose width is d and whose hole width is h
    '''
    ...


def signum( x ) :
    ''' Function parameter x is a numeric value. The function does not print
        any output. The function returns integer -1, 0, or 1 depending
        respectively whether x is negative, zero, or positive.
    '''

    ...

def mid( s ) :
    ''' Function parameter s is a string. If the length of s is odd, the function
        returns the middle character of s; otherwise, the function returns the
        two middle characters of s.
    '''

    ...