How to combine python scripts by parameterizing them?

Question

I have multiple scripts that calculates the different means given a list of numbers as arguments when calling the python script (https://github.com/alvations/meanie):

For example, harmonic_mean():

# -*- coding: utf-8 -*-

import math

def harmonic_mean(x): # x is a list of values.
  """ Returns the harmonic mean given a list of values. """
  return len(x) / sum([1/i for i in x])

def main(means):
  print "Input:", means
  means = map(float,means)
  print "harmonic mean = ", harmonic_mean(means)

if __name__ == '__main__':
  import sys
  if len(sys.argv) < 2:
    sys.stderr.write('Usage: python %s mean1 mean2 mean3 ... \n' % sys.argv[0])
    sys.exit(1)
  main(sys.argv[1:])

and root_mean_square()

# -*- coding: utf-8 -*-

import math

def root_mean_square(x): # x is a list of values.
  """ Returns the root mean square (rms) given a list of values. """
  return math.sqrt(sum([i*i for i in x])/len(x))

def main(means):
  print "Input:", means
  means = map(float,means)
  print "root mean square = ", root_mean_square(means)

if __name__ == '__main__':
  import sys
  if len(sys.argv) < 2:
    sys.stderr.write('Usage: python %s mean1 mean2 mean3 ... \n' % sys.argv[0])
    sys.exit(1)
  main(sys.argv[1:])

As you see, the two script does exactly the same thing but just calling different mean() functions and prints different outputs at the main(). How could I combine them and allow users to give a mean option parameter/argument when they call it at the console/terminal? E.g. the combined script is call meannie.py :

$ python meanie.py harmonic 1 2 3
$ python meanie.py hm 1 2 3

The above command should give the same output as calling (this is how users call the harmonic_mean() script now):

$ python hm.py 1 2 3

Matthew Trevor · Accepted Answer · 2014-02-03 05:33:20Z

Python has first-class functions; they're objects like everything else and can be passed around in the same way. So you just need a way of mapping the user input onto the specified function and then pass it into your main function:

def harmonic_mean(x):
    ...

def root_mean_square(x):
    ...

MEAN_FUNCS_MAP = {
    'hm': harmonic_mean,
    'harmonic': harmonic_mean,
    'rms':  root_mean_square,
}

def main(mean_fn, means):
    print "Input:", means
    means = map(float,means)
    print "root mean square = ", mean_fn(means)    

if __name__ == '__main__':
    import sys
    if len(sys.argv) < 3 or sys.argv[1] not in MEAN_FUNCS_MAP:
        sys.stderr.write('Usage: python %s <function> <mean1> <mean2> <mean3> ... \n' % sys.argv[0])
        sys.exit(1)
    main( MEAN_FUNCS_MAP[sys.argv[1]], sys.argv[2:] )

You should possibly also take a look at the argparse module, it's a lot less error prone than rolling your own command line interface.

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