"""
 doctest_function_example.py
"""

def double(x):
    """ Return 2 times x 
        >>> double(20)
        40
        >>> double('hey')
        'heyhey'
    """
    return 2 * x

def main():
    value = input("What is the value? ")
    print("You said ", value, "; double that is ", double(value))
    print()
    # See https://www.pinterest.com/pin/456200637224910893/
    print('And just for fun ...') 
    print(double(double(double('na'))), " batman! \n\n", end='')

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