Automated CWL and Galaxy XML generation for Python tools that use argparse and click
Switch branches/tags
Nothing to show
Clone or download
Pull request Compare This branch is 1 commit ahead, 92 commits behind erasche:master.
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.

gxargparse was originally designed to generate Galaxy XML from Python tools which use argparse, but then it was extended to support [Common Workflow Language] ( command-line tools generation, and not only for argparse, but also for click argument parser. For more info about CWL generation jump straight to argparse2cwl.


Galaxy argparse aims to be a drop-in replacement for argparse, quite literally. You can write use your normal import

import argparse

and continue writing code. All functions are passed straight through to argparse, but gxargparse captures them and copies some information along the way. This information captured is used to produce Galaxy Tool XML when it's requested with the --generate_galaxy_xml flag.

How it works

Internally, gxargparse, masquerading as argparse attempts to find and import the real argparse. It then stores a reference to the code module for the system argparse, and presents the user with all of the functions that stdlib's argparse provides. Every function call is passed through the system argparse. However, gxargparse captures the details of those calls and when Tool XML is requested, it builds up the tool definition according to IUC tool standards.


You can see the file for an example with numerous types of arguments and options that you might see in real tools. Accordingly there is an example.xml file with the output.

It doesn't work!!

If you are not able to use the --generate_galaxy_xml flag after installing, it is probably because of module load order. gxargparse must precede argparse in the path. Certain cases seem to work correctly (python install in a virtualenv) while other cases do not (pip install gxargparse).

To easily correct this, run the tool gxargparse_check_path which is installed as part of this package. Correctly functioning paths will produce the following:

$ gxargparse_check_path
Ready to go!

while incorrectly ordered paths will produce a helpful error message:

$ gxargparse_check_path
Incorrect ordering, please set


This can even be used inline:

user@host:$ PYTHONPATH=$(gxargparse_check_path -q) python --generate_galaxy_xml


This code doesn't cover the entirety of the argparse API yet, and there are some bugs to work out on the XML generation side:

  • argparse
    • groups not supported (in galaxy, everything should still work in argparse)
    • some features like templating of the version string (please submit bugs)
  • galaxyxml
    • bugs in conditionals/whens (probably)
    • bugs, bugs, bugs!
  • gxargparse
    • support help text
    • support declaring output files in an argparse-esque manner


argparse2cwl forms CWL tool descriptions from programs which use argparse as their argument parser. No code changes are required, just use the normal import:

import argparse

and continue writing code. All functions are passed straight through to argparse, but argparse2cwl captures them and copies some information along the way. This information captured is used to produce CWL tool definition when it's requested with the --generate_cwl_tool flag.


Installation process:

  1. Clone the source repository:

     $ git clone
  2. Run

     $ cd gxargparse
     $ python install

You can ensure it's working when you pass --help_arg2cwl flag to any command-line program inside your environment. If the option is not recognized, try

$ gxargparse_check_path

which is installed as part of this package. It will produce a helpful error message if the paths are incorrectly ordered. Also make sure you have installed it under proper Python version.


To run argparse2cwl, call your tool as usually without actual arguments with --generate_cwl_tool option:

$ <tool command> --generate_cwl_tool <other options>

Simple example

$ python --generate_cwl_tool

Example for CNVkit toolkit:

$ batch --generate_cwl_tool -d ~/cnvkit-tools/ --generate_outputs

If there are subcommands in the provided command, all possible tools will be generated, for instance, for CNVkit

$ --generate_cwl_tool

will produce CWL tool descriptions for batch, access, export bed, export cdt and all other subcommands.

Other options (which work only with --generate_cwl_tool provided, except for help message) are:

  • -o FILENAME, --output_section FILENAME: File with manually filled output section which is put to a formed CWL tool. Argparse2cwl is not very good at generating outputs, it recognizes output files only if they have type argparse.FileType('w'), so output section is often blank and should be filled manually.

  • -go, --generate_outputs: flag for generating outputs not only from arguments that are instances of argparse.FileType('w'), but also from every argument which contains output keyword in its name. For instance, argument --output-file with no type will also be placed to output section. However, '--output-directory' argument will also be treated like File, so generated tools must be checked carefully if when this option is selected.

  • -b, basecommand: command which appears in basecommand field in a resulting tool. It is handy to use this option when you run tool with shebang, but want python to be in basecommand field and the file amidst arguments. Example:

    $ --generate_cwl_tool -b python.

Basecommand of the formed tool will be ['python'], and search will be a positional argument on position 0.

  • -d, --directory: directory for storing tool descriptions.

  • --help_arg2cwl: prints this help message.

Argparse notes

Some of argparse features can not be ported to CWL.

  1. nargs=N. Number of arguments can not be specified in CWL (yet).
  2. const argument of add_argument(). All constants must be specified in job files.
  3. Custom types and custom actions are not supported.
  4. Argument groups don't work in CWL as arguments are sorted with a special algorithm
  5. Mutual exclusion is not supported.


click2cwl shares absolutely the same logic as argparse2cwl, the only difference is it is adjusted to work with click argument parser. Whenever click is imported, gxargparse grabs its commands, arguments, options and forms CWL parameters out of them.


  • Apache License, v2