How to read/process command line arguments?

by

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?

Contents hide
Related
Answers:
Method 1
Method 2
Method 3
Method 4
Method 5
Method 6
Method 7
Method 8
Method 9
Method 10
Method 11
Method 12
Method 13
Method 14
Method 15
Method 16
Method 17
Method 18
Method 19
Method 20

Related

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

import sys

print("n".join(sys.argv))

sys.argv is a list that contains all the arguments passed to the script on the command line. sys.argv[0] is the script name.

Basically,

import sys
print(sys.argv[1:])

Method 2

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.

Method 3

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

Method 4

There is also argparse stdlib module (an “impovement” on stdlib’s optparse module). Example from the introduction to argparse:

# script.py
import argparse

if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument(
        'integers', metavar='int', type=int, choices=range(10),
         nargs='+', help='an integer in the range 0..9')
    parser.add_argument(
        '--sum', dest='accumulate', action='store_const', const=sum,
        default=max, help='sum the integers (default: find the max)')

    args = parser.parse_args()
    print(args.accumulate(args.integers))

Usage:

$ script.py 1 2 3 4
4

$ script.py --sum 1 2 3 4
10

Method 5

If you need something fast and not very flexible

main.py:

import sys

first_name = sys.argv[1]
last_name = sys.argv[2]
print("Hello " + first_name + " " + last_name)

Then run python main.py James Smith

to produce the following output:

Hello James Smith

Method 6

One way to do it is using sys.argv. This will print the script name as the first argument and all the other parameters that you pass to it.

import sys

for arg in sys.argv:
    print arg

Method 7

The docopt library is really slick. It builds an argument dict from the usage string for your app.

Eg from the docopt readme:

"""Naval Fate.

Usage:
  naval_fate.py ship new <name>...
  naval_fate.py ship <name> move <x> <y> [--speed=<kn>]
  naval_fate.py ship shoot <x> <y>
  naval_fate.py mine (set|remove) <x> <y> [--moored | --drifting]
  naval_fate.py (-h | --help)
  naval_fate.py --version

Options:
  -h --help     Show this screen.
  --version     Show version.
  --speed=<kn>  Speed in knots [default: 10].
  --moored      Moored (anchored) mine.
  --drifting    Drifting mine.

"""
from docopt import docopt


if __name__ == '__main__':
    arguments = docopt(__doc__, version='Naval Fate 2.0')
    print(arguments)

Method 8

#set default args as -h , if no args:
if len(sys.argv) == 1: sys.argv[1:] = ["-h"]

Method 9

I use optparse myself, but really like the direction Simon Willison is taking with his recently introduced optfunc library. It works by:

“introspecting a function
definition (including its arguments
and their default values) and using
that to construct a command line
argument parser.”

So, for example, this function definition:

def geocode(s, api_key='', geocoder='google', list_geocoders=False):

is turned into this optparse help text:

    Options:
      -h, --help            show this help message and exit
      -l, --list-geocoders
      -a API_KEY, --api-key=API_KEY
      -g GEOCODER, --geocoder=GEOCODER

Method 10

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).

Method 11

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

Method 12

Pocoo’s click is more intuitive, requires less boilerplate, and is at least as powerful as argparse.

The only weakness I’ve encountered so far is that you can’t do much customization to help pages, but that usually isn’t a requirement and docopt seems like the clear choice when it is.

Method 13

import argparse

parser = argparse.ArgumentParser(description='Process some integers.')
parser.add_argument('integers', metavar='N', type=int, nargs='+',
                   help='an integer for the accumulator')
parser.add_argument('--sum', dest='accumulate', action='store_const',
                   const=sum, default=max,
                   help='sum the integers (default: find the max)')

args = parser.parse_args()
print(args.accumulate(args.integers))

Assuming the Python code above is saved into a file called prog.py
$ python prog.py -h

Ref-link: https://docs.python.org/3.3/library/argparse.html

Method 14

You may be interested in a little Python module I wrote to make handling of command line arguments even easier (open source and free to use) – Commando

Method 15

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.

Method 16

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.

Method 17

Also with python3 you might find convenient to use Extended Iterable Unpacking to handle optional positional arguments without additional dependencies:

try:
   _, arg1, arg2, arg3, *_ = sys.argv + [None] * 2
except ValueError:
   print("Not enough arguments", file=sys.stderr) # unhandled exception traceback is meaningful enough also
   exit(-1)

The above argv unpack makes arg2 and arg3 “optional” – if they are not specified in argv, they will be None, while if the first is not specified, ValueError will be thouwn:

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    _, arg1, arg2, arg3, *_ = sys.argv + [None] * 2
ValueError: not enough values to unpack (expected at least 4, got 3)

Method 18

My solution is entrypoint2. Example:

from entrypoint2 import entrypoint
@entrypoint
def add(file, quiet=True): 
    ''' This function writes report.

    :param file: write report to FILE
    :param quiet: don't print status messages to stdout
    '''
    print file,quiet

help text:

usage: report.py [-h] [-q] [--debug] file

This function writes report.

positional arguments:
  file         write report to FILE

optional arguments:
  -h, --help   show this help message and exit
  -q, --quiet  don't print status messages to stdout
  --debug      set logging level to DEBUG

Method 19

import sys

# Command line arguments are stored into sys.argv
# print(sys.argv[1:])

# I used the slice [1:] to print all the elements except the first
# This because the first element of sys.argv is the program name
# So the first argument is sys.argv[1], the second is sys.argv[2] ecc

print("File name: " + sys.argv[0])
print("Arguments:")
for i in sys.argv[1:]:
    print(i)

Let’s name this file command_line.py and let’s run it:

C:Userssimone> python command_line.py arg1 arg2 arg3 ecc
File name: command_line.py
Arguments:
arg1
arg2
arg3
ecc

Now let’s write a simple program, sum.py:

import sys

try:
    print(sum(map(float, sys.argv[1:])))
except:
    print("An error has occurred")

Result:

C:Userssimone> python sum.py 10 4 6 3
23

Method 20

Several of our biotechnology clients have posed these two questions recently:

  • How can we execute a Python script as a command?
  • How can we pass input values to a Python script when it is executed as a command?

I have included a Python script below which I believe answers both of these questions. Let’s assume the following Python script is saved in the file test.py:

#
#----------------------------------------------------------------------
#
# file name: test.py
#
# input values: data  - location of data to be processed
#               date  - date data were delivered for processing
#               study - name of the study where data originated
#               logs  - location where log files should be written 
#
# macOS usage: 
#
#   python3 test.py "/Users/lawrence/data" "20220518" "XYZ123" "/Users/lawrence/logs"
#
# Windows usage: 
#
#   python test.py "D:data" "20220518" "XYZ123" "D:logs"
#
#----------------------------------------------------------------------
#
# import needed modules...
#
import sys
import datetime

def main(argv):

   #
   # print message that process is starting...
   #
   print("test process starting at", datetime.datetime.now().strftime("%Y%m%d %H:%M"))

   #
   # set local values from input values...
   #
   data = sys.argv[1]
   date = sys.argv[2]
   study = sys.argv[3]
   logs = sys.argv[4]

   #
   # print input arguments...
   #
   print("data value is", data)
   print("date value is", date)
   print("study value is", study)
   print("logs value is", logs)

   #
   # print message that process is ending...
   #
   print("test process ending at", datetime.datetime.now().strftime("%Y%m%d %H:%M"))

#
# call main() to begin processing...
#

if __name__ == '__main__':

   main(sys.argv)

The script can be executed on a macOS computer in a Terminal shell as shown below and the results will be printed to standard output (be sure the current directory includes the test.py file):

$ python3 test.py "/Users/lawrence/data" "20220518" "XYZ123" "/Users/lawrence/logs"
test process starting at 20220518 16:51
data value is /Users/lawrence/data
date value is 20220518
study value is XYZ123
logs value is /Users/lawrence/logs
test process ending at 20220518 16:51

The script can also be executed on a Windows computer in a Command Prompt as shown below and the results will be printed to standard output (be sure the current directory includes the test.py file):

D:scripts>python test.py "D:data" "20220518" "XYZ123" "D:logs"
test process starting at 20220518 17:20
data value is D:data
date value is 20220518
study value is XYZ123
logs value is D:logs
test process ending at 20220518 17:20

This script answers both of the questions posed above and is a good starting point for developing scripts that will be executed as commands with input values.


All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

0 0 votes
Article Rating
Subscribe
Notify of
guest

0 Comments
Oldest
Newest Most Voted
Inline Feedbacks
View all comments
0
Would love your thoughts, please comment.x
()
x