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Python Pattern Matching

Python, I love you. But I'd like you to change. It's not you, it's me. Really. See, you don't have pattern matching. But, that's not the root of it. Macros are the root of it. You don't have macros but that's OK. Right now, I want pattern matching. I know you offer me if/elif/else statements but I need more. I'm going to abuse your functions. Guido, et al, I hope you can forgive me. This will only hurt a little.

Python Pattern Matching is an Apache2 licensed Python module for pattern matching like that found in functional programming languages. Most projects that address Python pattern matching focus on syntax and simple cases. Operator overloading is often used to change the semantics of operators to support pattern matching. In other cases, function decorators are used to implement multiple dispatch, sometimes known as function overloading. Each of these syntaxes, operators, and decorators, is really more of a detail in the application of pattern matching.

A lot of people have tried to make this work before. Somehow it didn't take. I should probably call this yet-another-python-pattern-matching-module but "yappmm" doesn't roll off the tongue. Other people have tried overloading operators and changing codecs. This module started as a codec hack but those are hard because they need an ecosystem of emacs-modes, vim-modes and the like to really be convenient.

Python Pattern Matching focuses instead on the semantics of pattern matching in Python. The dynamic duck-typing behavior in Python is distinct from the tagged unions found in functional programming languages. Rather than trying to emulate the behavior of functional pattern matching, this project attempts to implement pattern matching that looks and feels native to Python. In doing so the traditional function call is used as syntax. There are no import hooks, no codecs, no AST transforms.

.. todo::

   Python ``match`` function example.

Finally, pythonic pattern matching! If you've experienced the feature before in "functional" languages like Erlang, Haskell, Clojure, F#, OCaml, etc. then you can guess at the semantics.

.. todo::

   Show the same code without ``patternmatching``.


Features

  • Pure-Python
  • Developed on Python 3.9
  • Tested on CPython 3.6, 3.7, 3.8, and 3.9
.. todo::

   - Fully Documented
   - 100% test coverage
   - Hours of stress testing


Quickstart

Installing Python Pattern Matching is simple with pip:

$ pip install patternmatching

You can access documentation in the interpreter with Python's built-in help function. The help works on modules, classes, and functions in pattern matching.

>>> from patternmatching import match, bind, bound, like
>>> help(match)                     # doctest: +SKIP

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Python Pattern Matching License

Copyright 2015-2021, Grant Jenks

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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Python pattern matching like functional languages.

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