Metadata-Version: 1.1
Name: enpassant
Version: 0.3.1
Summary: En passant assignment for clearer if and while control structures
Home-page: https://bitbucket.org/jeunice/enpassant
Author: Jonathan Eunice
Author-email: jonathan.eunice@gmail.com
License: UNKNOWN
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        Many languages support *en passant* (in passing) assignment, like so::
        
            if result = expensive_request():
                print result.report()
        
        Python does not. This leads to more code lines and (in my opinion) less visual
        clarity::
        
            result = expensive_request()
            if result:
                print result.report()
        
        Or worse, in the case of looping structures::
        
            result = expensive_request()
            while result:
                print result.report()
                result = expensive_request()
        
        It doesn't look so bad here, in a highly distilled example, but in real
        programs, the called function often has parameters to be managed, and the
        surrounding code is invariably longer and more complicated. The more
        complicated the surrounding computations and requests, the simpler the
        comparison itself should be. As the `Zen of Python
        <http://www.python.org/dev/peps/pep-0020/>`_ intones: "Simple is better than
        complex." and "Readability counts."
        
        I hope that Python
        will eventually provide a concise way of handling this, such as::
        
            while expensive_request() as result:
                print result.report()
        
        But in the meanwhile, ``enpassant`` provides a workaround.
        
        Usage
        =====
        
        ::
        
            from enpassant import *
            result = Passer()
        
            while result / expensive_request():
                print result.report()
        
        ``result`` is merely a proxy object that, when it encounters the division
        operator, returns the denominator. That is, ``result / whatever ==
        whatever``. But it also *remembers* the denominator value. Then, whenever
        you want the result value provided (presumably, later in the body of your
        loop or conditional), simply access it through ``result``. If you want the
        full object returned by ``expensive_request()`` you can get it via
        ``result.value``. Or or the result has items or attributes, they are
        available by indexing or naming the attribute directly. *Easy peasy!*
        
        NB: If you change the items or attributes of ``result``, those settings are
        also forwarded to the underlying object. ``result`` is not a copy, but a
        true proxy, and as close to the actual object returned as I can make it
        given current Python strictures.
        
        Some Details
        ============
        
        ``enpassant`` "assignment" is transparent to conditional expressions,
        because the value of the expression is always the value of the denominator.
        But ``Passers`` are also guaranteed to have a Boolean value identical to
        that of the value they contain, should you wish to use them in subsequent
        tests.
        
        The ``result`` in the example above isn't the pure result of the following
        function call (or expression), but rather a proxy to it. While item (``[]``)
        and attribute (``.``) access work directly on ``result``, this is because
        ``Passer`` objects pass on *getitem* and *get-attribute* requests to their
        enclosed value. Usually, this is a convenience, and avoids having to
        needlessly state that it's really ``result.value`` that's being indexed or
        dereferenced. But if you need the specific object returned (say for an
        object identity or ``isinstance`` test, use ``result.value`` directly.
        
        Alternative Value Access
        ========================
        
        It is also possible to retrieve the value of a ``Passer`` by calling it::
        
            if result / expensive_request():
                print result().report()
        
        This technique makes clear that the value is being rendered via some
        process, rather than just presented as a normal Python name / variable. And
        the resulting object from ``result()`` is the true and complete result of
        the earlier function call, with no need for implicit / auto-magical
        forwarding of items and attributes. Which style makes sense is a matter of
        judgment and taste.
        
        Or, if you prefer something terser, the ``+`` (unary positive) operation
        will also yield the value::
        
            if result / expensive_request():
                print +result.report()
        
        Alternative Operations
        ======================
        
        .. |larrow| unicode:: 0x2190 .. leftwards arrow
        
        If you prefer the less-than (``<``) or less-than-or-equal (``<=``) operators
        as indicators that ``result`` takes the value of the following value, they
        are supported as aliases of the division operation (``/``). Thus, the
        following are identical::
        
            if result / expensive_request():
                print result.report()
        
            if result < expensive_request():
                print result.report()
        
            if result <= expensive_request():
                print result.report()
        
        It's a matter of preference which seems most logical, appropriate, and
        expressive.
        None of them are as good
        Note, however, that the operation usually known as division
        (``/``) has a much higher precedence (i.e. tighter binding to its operands)
        than the typical comparison operations (``<`` and ``<=``). If used with a
        more complex expressions, either know your precedence or use parenthesis to
        disambiguate!
        
        It'd be swell if Python supported arbitrary symbols. Unicode has what would
        be reasonable alternative assignment markers, such as |larrow| (`LEFTARDS
        ARROW <http://www.fileformat.info/info/unicode/char/2190/index.htm>`_), but
        alas! Until Python gets more Unicode-savvy, we have to choose some existing
        ASCII operator to repurpose.
        
        Grabber and Similar
        ===================
        
        I've begun experimenting with other forms of collecting and rendering values.
        This version of ``enpassant`` includes the results of one of those experiments.
        Objects of the ``Grabber`` class can have their attributes set on their first
        access. Subsequent uses of that attribute yield the set value.::
        
            info = Grabber()
            info.name('Joe')
            assert info.name == 'Joe'
        
        The challenge with this approach is that once set, attribute values cannot be
        reset.
        
        Notes
        =====
        
         *  `En passant <http://en.wikipedia.org/wiki/En_passant>`_ is a chess
            term.
        
         *  En passant assignment / naming is discussed in
            `Issue1714448 <http://bugs.python.org/issue1714448>`_
            and `PEP 379 <http://www.python.org/dev/peps/pep-0379/>`_, which have
            been rejected and withdrawn, respectively. But that is years gone
            by. I hope the idea will be productively reconsidered in the future.
        
         *  Automated multi-version testing managed with the wonderful
            `pytest <http://pypi.python.org/pypi/pytest>`_,
            and `tox <http://pypi.python.org/pypi/tox>`_.
            Successfully packaged for, and tested against, all late-model versions of
            Python: 2.6, 2.7, 3.2, 3.3, 3.4, 3.5a4, as well as PyPy 2.5.1 (based on 2.7.9)
            and PyPy3 2.4.0 (based on 3.2.5).
            Test line coverage ~100%.
        
         *  On Python 2.6, uses Raymond Hettinger's `ordereddict <https://pypi.python.org/pypi/ordereddict>`_
            module (which is included in the source tree for ease of installation)
            to provide ``OrderedDict``. Thank you, Raymond!
        
         *  The `simplere <http://pypi.python.org/pypi/simplere>`_
            package similarly provides
            en passant handling (and other helpers) for the important,
            common case of regular expression
            searches.
        
         *  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 enpassant
        
        To ``easy_install`` under a specific Python version (3.3 in this example)::
        
            python3.3 -m easy_install --upgrade enpassant
        
        (You may need to prefix these with "sudo " to authorize installation. In
        environments without super-user privileges, you may want to use ``pip``'s
        ``--user`` option, to install only for a single user, rather than
        system-wide.)
Keywords: en passant
Platform: UNKNOWN
Classifier: Development Status :: 3 - Alpha
Classifier: Operating System :: OS Independent
Classifier: License :: OSI Approved :: BSD License
Classifier: Intended Audience :: Developers
Classifier: Programming Language :: Python
Classifier: Programming Language :: Python :: 2.6
Classifier: Programming Language :: Python :: 2.7
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.3
Classifier: Programming Language :: Python :: 3.4
Classifier: Programming Language :: Python :: Implementation :: CPython
Classifier: Programming Language :: Python :: Implementation :: PyPy
Classifier: Topic :: Software Development :: Libraries :: Python Modules
