# Contributing to Pyparsing

Thank you for your interest in working on pyparsing! Pyparsing has become a popular module for creating simple text parsing and data scraping applications. It has been incorporated in several widely-used packages, and is often used by beginners as part of their first Python project.

## Raising questions / asking for help

If you have a question on using pyparsing, there are a number of resources available online.

- StackOverflow - about 10 years of SO questions and answers can be searched on StackOverflow, tagged with the `pyparsing` tag. Note that some of the older posts will refer to features in Python 2, or to versions and coding practices for pyparsing that have been replaced by newer classes and coding idioms.

- pyparsing sub-reddit - still very lightly attended, but open to anyone wishing to post questions or links related to pyparsing. An alternative channel to StackOverflow for asking questions.

- online docs and a separately maintained set of class library docs here - These docs are auto-generated from the docstrings embedded in the pyparsing classes, so they can also be viewed in the interactive Python console’s and Jupyter Notebook’s `help` commands.

- the pyparsing Wikispaces archive - Before hosting on GitHub, pyparsing had a separate wiki on the wikispaces.com website. In 2018 this page was discontinued. The discussion content archive has been reformatted into Markdown and can be viewed by year at the GitHub repository. Just as with some of the older questions on StackOverflow, some of these older posts may reflect out-of-date pyparsing and Python features.

- submit an issue - If you have a problem with pyparsing that looks like an actual bug, or have an idea for a feature to add to pyparsing please submit an issue on GitHub. Some pyparsing behavior may be counter-intuitive, so try to review some of the other resources first, or some of the other open and closed issues. Or post your question on SO or reddit. But don’t wait until you are desperate and frustrated - just ask! :)

## Submitting examples

If you have an example you wish to submit, please follow these guidelines.

- License - Submitted example code must be available for distribution with the rest of pyparsing under the MIT open source license.

- Please follow PEP8 name and coding guidelines, and use the black formatter to auto-format code.

- Examples should import pyparsing and the common namespace classes as:

      import pyparsing as pp
      # if necessary
      ppc = pp.pyparsing_common
      ppu = pp.pyparsing_unicode

- Submitted examples must be Python 3.9 or later compatible. (It is acceptable if examples use Python features added after 3.6)

- Where possible use operators to create composite parse expressions:

      expr = expr_a + expr_b | expr_c

  instead of:

      expr = pp.MatchFirst([pp.And([expr_a, expr_b]), expr_c])

  Exception: if using a generator to create an expression:

      import keyword
      python_keywords = keyword.kwlist
      any_keyword = pp.MatchFirst(pp.Keyword(kw)
                                  for kw in python_keywords))

- Learn Common Pitfalls When Writing Parsers and how to avoid them when developing new examples.

- See additional notes under Some coding points.

## Submitting changes

If you are considering proposing updates to pyparsing, please bear in mind the following guidelines.

Please review The Zen of Pyparsing and The Zen of Pyparsing Development article on the pyparsing wiki, to get a general feel for the historical and future approaches to pyparsing’s design, and intended developer experience as an embedded DSL.

If you are using new Python features or changing usage of the Python stdlib, please check that they work as intended on prior versions of Python (currently back to Python 3.6.8).

## Some design points

- Minimize additions to the module namespace. Over time, pyparsing’s namespace has acquired a lot of names. New features have been encapsulated into namespace classes to try to hold back the name flooding when importing pyparsing.

- New operator overloads for ParserElement will need to show broad applicability, and should be related to parser construction.

- Performance tuning should focus on parse time performance. Optimizing parser definition performance is secondary.

- New external dependencies will require substantial justification, and if included, will need to be guarded for `ImportError`s raised if the external module is not installed.

## Some coding points

These coding styles are encouraged whether submitting code for core pyparsing or for submitting an example.

- PEP8 - pyparsing has historically been very non-compliant with many PEP8 guidelines, especially those regarding name casing. I had just finished several years of Java and Smalltalk development, and camel case seemed to be the future trend in coding styles. As of version 3.0.0, pyparsing is moving over to PEP8 naming, while maintaining compatibility with existing parser code by defining synonyms using the legacy names. These names will be retained until a future release (probably 4.0), to provide a migration path for current pyparsing-dependent applications - DO NOT MODIFY OR REMOVE THESE NAMES. See more information at the PEP8 wiki page.

- No backslashes for line continuations. Continuation lines for expressions in `()`’s should start with the continuing operator:

      really_long_line = (
          something
          + some_other_long_thing
          + even_another_long_thing
      )

- Maximum line length is 120 characters. (Black will override this.)

- Changes to core pyparsing must be compatible back to Py3.6 without conditionalizing. Later Py3 features may be used in examples by way of illustration.

- `str.format()` statements should use named format arguments (unless this proves to be a slowdown at parse time).

- List, tuple, and dict literals should include a trailing comma after the last element, which reduces changeset clutter when another element gets added to the end.

- New features should be accompanied by updates to `unitTests.py` and a bullet in the CHANGES file.

- Do not modify `pyparsing_archive.py`. This file is kept as a reference artifact from when pyparsing was distributed as a single source file.

## Some documentation points

- The docstrings in pyparsing (which are generated into the package’s API documentation by Sphinx) make heavy use of doctests for their example code. This allows examples to be tested and verified as working, and ensures that any changes to the code which affect output are accompanied by corresponding changes in the examples.

- The codebase’s docstring tests can be verified by running the command `make doctest` from the `docs/` directory. The output should ideally look something like this:

      $ make doctest
      [...documentation build...]
      running tests...

      Document: pyparsing
      -------------------
      1 item passed all tests:
       204 tests in default
      204 tests in 1 item.
      204 passed.
      Test passed.

      Document: whats_new_in_3_1
      --------------------------
      1 item passed all tests:
        15 tests in default
      15 tests in 1 item.
      15 passed.
      Test passed.

      Doctest summary
      ===============
        219 tests
          0 failures in tests
          0 failures in setup code
          0 failures in cleanup code

  Any failed tests will be displayed in detail.

- Much more information about doctests can be found in the Pyparsing documentation, in the chapter titled “Writing doctest examples”. Even if you have never worked with them before, it should guide you through everything you need to know in order to write Pyparsing doctest examples. If you are already familiar with doctests and with `sphinx.ext.doctest` in general, you may wish to skip over the introductory content and go straight to the section on “Doctests in Pyparsing” which covers some issues specific to the project.