How to read/process command line arguments?

Question

I am originally a C programmer. I have seen numerous tricks and "hacks" to read many different arguments.

What are some of the ways Python programmers can do this?

Related

• What’s the best way to grab/parse command line arguments passed to a Python script?
• Implementing a “[command] [action] [parameter]” style command-line interfaces?
• How can I process command line arguments in Python?
• How do I format positional argument help using Python’s optparse?

Answer 1

The canonical solution in the standard library is argparse (docs):

Here is an example:

from argparse import ArgumentParser

parser = ArgumentParser()
parser.add_argument("-f", "--file", dest="filename",
                    help="write report to FILE", metavar="FILE")
parser.add_argument("-q", "--quiet",
                    action="store_false", dest="verbose", default=True,
                    help="don't print status messages to stdout")

args = parser.parse_args()

argparse supports (among other things):

• Multiple options in any order.
• Short and long options.
• Default values.
• Generation of a usage help message.

Answer 2

As you can see optparse "The optparse module is deprecated with and will not be developed further; development will continue with the argparse module."

Answer 3

Yet another option is argh. It builds on argparse, and lets you write things like:

import argh

# declaring:

def echo(text):
    "Returns given word as is."
    return text

def greet(name, greeting='Hello'):
    "Greets the user with given name. The greeting is customizable."
    return greeting + ', ' + name

# assembling:

parser = argh.ArghParser()
parser.add_commands([echo, greet])

# dispatching:

if __name__ == '__main__':
    parser.dispatch()

It will automatically generate help and so on, and you can use decorators to provide extra guidance on how the arg-parsing should work.

Answer 4

I recommend looking at docopt as a simple alternative to these others.

docopt is a new project that works by parsing your --help usage message rather than requiring you to implement everything yourself. You just have to put your usage message in the POSIX format.

Answer 5

I like getopt from stdlib, eg:

try:
    opts, args = getopt.getopt(sys.argv[1:], 'h', ['help'])
except getopt.GetoptError, err: 
    usage(err)

for opt, arg in opts:
    if opt in ('-h', '--help'): 
        usage()

if len(args) != 1:
    usage("specify thing...")

Lately I have been wrapping something similiar to this to make things less verbose (eg; making "-h" implicit).

Answer 6

Just going around evangelizing for argparse which is better for these reasons.. essentially:

(copied from the link)

• argparse module can handle positional and optional arguments, while optparse can handle only optional arguments

• argparse isn’t dogmatic about what your command line interface should look like - options like -file or /file are supported, as are required options. Optparse refuses to support these features, preferring purity over practicality

• argparse produces more informative usage messages, including command-line usage determined from your arguments, and help messages for both positional and optional arguments. The optparse module requires you to write your own usage string, and has no way to display help for positional arguments.

• argparse supports action that consume a variable number of command-line args, while optparse requires that the exact number of arguments (e.g. 1, 2, or 3) be known in advance

• argparse supports parsers that dispatch to sub-commands, while optparse requires setting allow_interspersed_args and doing the parser dispatch manually

And my personal favorite:

• argparse allows the type and action parameters to add_argument() to be specified with simple callables, while optparse requires hacking class attributes like STORE_ACTIONS or CHECK_METHODS to get proper argument checking