what is __doc__ - python

def print_max(x, y):
    '''
    Writing the bigest int
    '''
    x = int(x)
    y = int(y)

    if x > y:
        print('%d is max %d is min' % (x, y))
    else:
        print('%d is max %d is min' % (y, x))

print_max(10, 511)
print(print_max.__doc__)