How to parse Python command arguments and options

July 24, 2015 by Zemian Deng Comment

Tags: python

https://docs.python.org/3/howto/argparse.html

The python doc for argparse module didn't provide enough examples on the usage. I also think the module and parser itself is TOO flexible, in that the add_argument function accept too many parameters and it's confusing to use.

In most cases, you would define structure of your program's input with two parts: Your program actual arguments and optional parameters. Then you would invoke the parser and use the result as a dict (Namespace) like object.

Here are few examples that demonstrate how to use it in few common cases.

Example0: Handle raw arguments

import sys
args = sys.argv[1:]

for name in args:
  print(name)

Example1: Handle 2 arguments and a boolean option

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('hostname', default='localhost')
parser.add_argument('port', default=12345, type=int)
parser.add_argument('-d', default=False, action='store_true')
args = parser.parse_args()

if args.d:
 print("Processing host %s on port %d" % (args.hostname, args.port))

Example2: Handle 1 argument with many options

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('url')
parser.add_argument('-u', '--user', help='user', default='demo')
parser.add_argument('-p', '--password', help='user password', default='demo123')
parser.add_argument('-l', '--limit', help='max limit value', default=1000, type=int)
parser.add_argument('--payload', help='text file payload', default='payload.xml')
args = parser.parse_args()

print("Processing url %s" % args.url)

user, password = args.user, args.password
print("Got option user=%s" % user)

with open(args.payload) as fh:
  payload = fh.read()

if args.limit > 100:
  print("Limit has exceed 100")


Example3: Handle one or more arguments with a boolean option

import argparse, fileinput
parser = argparse.ArgumentParser()
parser.add_argument('files', metavar='FILE', nargs='+')
parser.add_argument('-d', default=False, action='store_true')
args = parser.parse_args()

for line in fileinput.input(args.files):
  if args.d:
    print("Processing line: %s" % line, end='')

To display the default values in the helppage, do this with the parser

parser = argparse.ArgumentParser(formatter_class=argparse.ArgumentDefaultsHelpFormatter)