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Intro

The library implements a regular expression engine based on nondeterministic finite automata (NFA). It uses the Thompson's construction algorithm to transform regular expressions into NFAs. No backreferences are used during the matching process which should make this engine much faster than the standard Python's re module.

Supported features:

  • common operators like *, +, ?, and |
  • ranges, e.g. [a-z]
  • groups, e.g. (abc)
  • starting and ending position indicators: ^ and $
  • the caret ^ operator

How to Install

Prerequisites:

  • Python version 3.6.6
  • virtualenv or Python 3 venv module (optional)

Create a virtual environment with virtualenv or venv in the directory with the library sources:

$ virtualenv venv  # virtualenv approach

or

$ python -m venv venv  # venv approach

Activate the environment with

$ . ./venv/bin/activate

and install the library

$ python setup.py install

Running Tests

To check the installation was successful, it will be a good idea to run the tests. The library uses pytest as a testing framework. If you've followed the instructions from the previous section, pytest is already installed in your virtual environment.

To run the tests do

$ pytest tests/

To get a test coverage report run

$ pytest --cov=regex tests/

A test coverage example report:

---------- coverage: platform darwin, python 3.6.6-final-0 -----------
Name                                                                       Stmts   Miss  Cover
----------------------------------------------------------------------------------------------
venv/lib/python3.6/site-packages/regex-0.1-py3.6.egg/regex/__init__.py         3      0   100%
venv/lib/python3.6/site-packages/regex-0.1-py3.6.egg/regex/compiler.py        92      4    96%
venv/lib/python3.6/site-packages/regex-0.1-py3.6.egg/regex/exceptions.py       2      0   100%
venv/lib/python3.6/site-packages/regex-0.1-py3.6.egg/regex/executor.py        25      0   100%
venv/lib/python3.6/site-packages/regex-0.1-py3.6.egg/regex/tokenizer.py      177     14    92%
----------------------------------------------------------------------------------------------
TOTAL                                                                        299     18    94%

API

The API is simple and consists of one function named match. The function takes a POSIX-like regular expression and a string and returns True or False depending on whether the string matcher the expression or not.

>>> from regex import match
>>> match(r'a|b', 'a')
True
>>> match(r'[a-z0-9]*(!+|\?+)123', 'aaa000999zzzbbb???123')
True
>>> match(r'foo', 'bar')
False

The function raises the MalformedRegex exception if the regular expression can't be parsed.

Command Line Tool

The library ships with the command line tool named regex. It is a simple app that takes a regular expression as its first argument and a string as the second. For example:

$ regex "a?a?b" "ab"
The string 'ab' matches

References

Regular Expression Matching Can Be Simple And Fast by Russ Cox.