Pass arguments from cmd to python script [duplicate]

I write my scripts in python and run them with cmd by typing in:

C:\> python script.py 

Some of my scripts contain separate algorithms and methods which are called based on a flag. Now I would like to pass the flag through cmd directly rather than having to go into the script and change the flag prior to run, I want something similar to:

C:\> python script.py -algorithm=2 

I have read that people use sys.argv for almost similar purposes however reading the manuals and forums I couldn't understand how it works.

3 Answers

There are a few modules specialized in parsing command line arguments: getopt, optparse and argparse. optparse is deprecated, and getopt is less powerful than argparse, so I advise you to use the latter, it'll be more helpful in the long run.

Here's a short example:

import argparse # Define the parser parser = argparse.ArgumentParser(description='Short sample app') # Declare an argument (`--algo`), saying that the # corresponding value should be stored in the `algo` # field, and using a default value if the argument # isn't given parser.add_argument('--algo', action="store", dest='algo', default=0) # Now, parse the command line arguments and store the # values in the `args` variable args = parser.parse_args() # Individual arguments can be accessed as attributes... print args.algo 

That should get you started. At worst, there's plenty of documentation available on line (say, this one for example)...

It might not answer your question, but some people might find it usefull (I was looking for this here):

How to send 2 args (arg1 + arg2) from cmd to python 3:

----- Send the args in test.cmd:

python "C:\Users\test.pyw" "arg1" "arg2" 

----- Retrieve the args in test.py:

print ("This is the name of the script= ", sys.argv[0]) print("Number of arguments= ", len(sys.argv)) print("all args= ", str(sys.argv)) print("arg1= ", sys.argv[1]) print("arg2= ", sys.argv[2]) 

Try using the getopt module. It can handle both short and long command line options and is implemented in a similar way in other languages (C, shell scripting, etc):

import sys, getopt def main(argv): # default algorithm: algorithm = 1 # parse command line options: try: opts, args = getopt.getopt(argv,"a:",["algorithm="]) except getopt.GetoptError: <print usage> sys.exit(2) for opt, arg in opts: if opt in ("-a", "--algorithm"): # use alternative algorithm: algorithm = arg print "Using algorithm: ", algorithm # Positional command line arguments (i.e. non optional ones) are # still available via 'args': print "Positional args: ", args if __name__ == "__main__": main(sys.argv[1:]) 

You can then pass specify a different algorithm by using the -a or --algorithm= options:

python <scriptname> -a2 # use algorithm 2 python <scriptname> --algorithm=2 # ditto 

See: getopt documentation