pipe_mass.py

import math


def area_of_circle(diameter):
    return math.pi * (diameter / 2 ** 2)


def volume_of_pipe(inner_diameter, outer_diameter, length):
    area_of_pipe_end = (
        area_of_circle(outer_diameter) -
        area_of_circle(inner_diameter)
    )
    return length * area_of_pipe_end


def weight_of_pipe(inner_diameter, outer_diameter, length, mass_per_unit):
    return (
        mass_per_unit *
        volume_of_pipe(inner_diameter, outer_diameter, length)
    )


def main():
    wop = weight_of_pipe(
        inner_diameter=9,
        outer_diameter=10,
        length=50,
        mass_per_unit=1
    )

    # old (c-like) syntax
    print('%.2f units' % wop)

    # new syntax
    print('{:.2f} units'.format(wop))


if __name__ == '__main__':
    main()