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

User · Answer

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)

User · Answer

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

User · Answer

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

User · Answer

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  lt name gt       naval fate py ship  lt name gt  move  lt x gt   lt y gt   --speed  lt kn gt     naval fate py ship shoot  lt x gt   lt y gt    naval fate py mine  set remove   lt x gt   lt y gt   --moored   --drifting    naval fate py  -h   --help    naval fate py --version  Options    -h --help     Show this screen    --version     Show version    --speed  lt kn gt   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

User · Answer

set default args as -h   if no args  if len sys argv     1  sys argv 1       -h

User · Answer

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   Basically   import sys print sys argv 1

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

[python] How to read/process command line arguments?

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