simple python script for calculator of chromatography

chrom_cal.py

import click

pi = 3.14

@click.group()
def cli():
    pass

@cli.command()
@click.option(
    '-l', '--linearflow', prompt='Linear flow (cm/h)?',
    type=int,
    help='The linear flow (cm/h) of your column.')
@click.option(
    '-d', '--diameter', prompt='column diameter in cm?',
    type=float,
    help='The column diameter of your column.')
def flowrate(linearflow, diameter):
    """
    Volumetric flow rate (ml/min) = [Linear flow (cm/h)/60] x column cross sectional area (cm2)
    """
    flowrate = (float(linearflow)/60.0)*(pi*(float(diameter)**2)/4.0)
    return click.echo(f'The flow rate is {flowrate} ml/min')

@cli.command()
@click.option(
    '-v', '--volumeflow', prompt='Volumetric flow rate (ml/min)?',
    type=float,
    help='The volumetric flow rate(ml/min) of your column.')
@click.option(
    '-d', '--diameter', prompt='column diameter in cm?',
    type=float,
    help='The column diameter of your column.')
def volumeflow(volumeflow, diameter):
    """
    Linear flow rate = [Volumetric flow rate (ml/min) × 60] / column cross sectional area (cm2)
    """
    volumeflow = float(volumeflow)*60.0*4/(pi*(float(diameter))**2)
    return click.echo(f'The linear flow is {volumeflow} cm/h')

@cli.command()
@click.option(
    '-l', '--linearflow', prompt='Linear flow (cm/h)?',
    type=int,
    help='The linear flow (cm/h) of your column.')
@click.option(
    '-h', '--bedhight', prompt='Bed height(cm)?',
    type=int,
    help='The bed heigt(cm) of your column.')
def residencetime(linearflow, bedhight):
    """Residence time (min) = [bed height (cm)/flow velocity (cm/h)] x 60"""
    residence_time = (bedhight/linearflow)*60.0
    return click.echo(f'The residence time is {residence_time} min.')

if __name__ == '__main__':
    cli()