simplere 1.0.2

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:target: https://travis-ci.org/jonathaneunice/simplere

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:target: https://crate.io/packages/simplere/

A simplified interface to Python's regular expression (``re``)
string search that tries to eliminate steps and provide
simpler access to results. As a bonus, also provides compatible way to
access Unix glob searches.

Usage
=====

Python regular expressions are powerful, but the language's lack
of an *en passant* (in passing) assignment requires a preparatory
motion and then a test::

import re

match = re.search(pattern, some_string)
if match:
print match.group(1)

With ``simplere``, you can do it in fewer steps::

from simplere import *

if match / re.search(pattern, some_string):
print match[1]

Or with an object-orented style:

if some_string in Re(pattern):
print Re._[1]


Re Objects
==========

``Re`` objects are `memoized
<http://en.wikipedia.org/wiki/Memoization>`_ for efficiency, so they compile their
pattern just once, regardless of how many times they're mentioned in a
program.

Note that the ``in`` test turns the sense of the matching around (compared to
the standard ``re`` module). It asks "is the given string *in*
the set of items this pattern describes?" To be fancy, the
``Re`` pattern is an intensionally
defined set (namely "all strings matching the pattern"). This order often makes
excellent sense whey you have a clear intent for the test. For example, "is the
given string within the set of *all legitimate commands*?"

Second, the ``in`` test had the side effect of setting the underscore
name ``_`` to the result. Python doesn't support *en passant* assignment--apparently,
no matter how hard you try, or how much introspection you use. This makes it
harder to both test and collect results in the same motion, even though that's
often exactly appropriate. Collecting them in a class variable is a fallback
strategy (see the *En Passant* section below for a slicker one).

If you prefer the more traditional ``re`` calls::

if Re(pattern).search(some_string):
print Re._[1]

``Re`` works even better with named pattern components, which are exposed
as attributes of the returned object::

person = 'John Smith 48'
if person in Re(r'(?P<name>[\w\s]*)\s+(?P<age>\d+)'):
print Re._.name, "is", Re._.age, "years old"
else:
print "don't understand '{}'".format(person)

One trick being used here is that the returned object is not a pure
``_sre.SRE_Match`` that Python's ``re`` module returns. Nor is it a subclass.
(That class `appears to be unsubclassable
<http://stackoverflow.com/questions/4835352/subclassing-matchobject-in-python>`_.)
Thus, regular expression matches return a proxy object that
exposes the match object's numeric (positional) and
named groups through indices and attributes. If a named group has the same
name as a match object method or property, it takes precedence. Either
change the name of the match group or access the underlying property thus:
``x._match.property``

It's possible also to loop over the results::

for found in Re('pattern (\w+)').finditer('pattern is as pattern does'):
print found[1]

Or collect them all in one fell swoop::

found = Re('pattern (\w+)').findall('pattern is as pattern does')

Pretty much all of the methods and properties one can access from the standard
``re`` module are available.

Bonus: Globs
============

Regular expressions are wonderfuly powerful, but sometimes the simpler `Unix glob
<http://en.wikipedia.org/wiki/Glob_(programming)>`_ is works just fine. As a bonus,
``simplere`` also provides simple glob access.::

if 'globtastic' in Glob('glob*'):
print "Yes! It is!"
else:
raise ValueError('YES IT IS')

En Passant
==========

If you have existing code that already uses ``re`` regular expressions
and you want to ease into using ``simplere``, ``ReMatch`` objects can
simply wrap Python's native``_sre.SRE_Match`` objects (the things that ``re``
method calls return).::

match = re.match(r'(?P<word>th.s)', 'this is a string')
match = ReMatch(match)
if match:
print match.group(1) # still works
print match[1] # same thing
print match.word # same thing, with logical name

But that's a huge amount of boiler plate for a simple test, right? So ``simplere``
also uses an *en passant* trick of redefining the division operation::

if match / re.search(r'(?P<word>th.s)', 'this is a string'):
assert match[1] == 'this'
assert match.word == 'this'
assert match.group(1) == 'this'

This uses the pre-delcared ``match`` object and the division operator (``/``)
to quickly funnel
the result of the search.
If the ``re`` operation fails, the resulting object is guaranteed to have
a ``False``-like boolean value, so that it will fall through conditional tests.

If you prefer the look of the less-than (``<``) or less-than-or-equal (``<=``),
as indicators that ``match`` takes the value of the following function call, they
are supported as aliases of the division operation (``/``). You may define your
own match objects, and can use them on memoized ``Re`` objects too. Putting
a few of these optional things together::

answer = Match() # need to do this just once

if answer < Re(r'(?P<word>th..)').search('and that goes there'):
assert answer.word == 'that'

Notes
=====

* Automated multi-version testing is managed with the wonderful
`pytest <http://pypi.python.org/pypi/pytest>`_
and `tox <http://pypi.python.org/pypi/tox>`_. ``simplere`` is
successfully packaged for, and tested against, all late-model verions of
Python: 2.6, 2.7, 3.2, and 3.3, as well as PyPy 1.9 (based on 2.7.2).

* ``simplere`` is one part of a larger effort to add intensional sets
to Python. The `intensional <http://pypi.python.org/pypi/intensional>`_
package contains a parallel implementation of ``Re``, among many other
things.

* The author, `Jonathan Eunice <mailto:jonathan.eunice@gmail.com>`_ or
`@jeunice on Twitter <http://twitter.com/jeunice>`_
welcomes your comments and suggestions.

Installation
============

To install the latest version::

pip install -U simplere

To ``easy_install`` under a specific Python version (3.3 in this example)::

python3.3 -m easy_install --upgrade simplere

(You may need to prefix these with "sudo " to authorize installation.)