D 2012-04-10T15:57:56
L Underscode
P db426bb1d8b1754e3cc4e6d38ce6cc8ab594a133
U ivan
W 5895
<h1>Underscode, a Python identifier-like encoding</h1>

<dl>
<dt>Author<dd><a href="mailto:ivan&#64;selidor.net">Ivan Vilata i Balaguer</a>
<dt>URL<dd>[https://elvil.net/fossil/underscode/]
</dl>


<h2>About Underscode</h2>

[https://elvil.net/fossil/underscode/|Underscode] is an encoding which is
capable of representing <em>any</em> Unicode string as a valid (and quite
similar) Python identifier.  The way Unicode strings are encoded minimises the
chances of clashing with other existing names, while not obscuring the
resulting string too much.

Some method decorators are provided which allow arbitrary objects to be
accessed as normal instance attributes, with optional tab-completion support
for interactive usage.  The standard Python codec API is also supported.

Underscode-encoded (or <em>underscoded</em>) strings can be quickly spotted
because they end with an <em>odd</em> number of underscores, and they contain
escape sequences beginning with an underscore where characters not allowed in
identifiers would be found.  Some examples of underscoded strings are:

<ul>
<li><code>_</code> encodes the empty string.
<li><code>foo_</code> encodes <code>foo</code>.
<li><code>class_</code> encodes <code>class</code>.
<li><code>foo__bar_</code> encodes <code>foo bar</code>.
<li><code>foo_x5fbar_</code> encodes <code>foo_bar</code>.
<li><code>_2006_09_18_</code>, like <code>_20060918_</code>, encodes <code>20060918</code>.
<li><code>_x2fbin_x2fls_</code>, encodes <code>/bin/ls</code>.
<li><code>The__Knights__Who__Say___u201cNi_x21_u201d_</code> encodes the properly quoted <code>The Knights Who Say “Ni!”</code>.
</ul>

As you see, underscoded strings are quite similar to their decoded
counterparts when these are more or less identifier-like, but complex strings
can still be handled.

Underscode is a very basic tool which may have several uses:

<ul>
<li>Avoiding clashes between method names and table field names in ORMs.
<li>Enabling interactive attribute-like completion for children in
hierarchically arranged structures (DOM trees, filesystems...), with full
Unicode support.
<li>As an aid in the generation of RPC stubs for identifiers which are not
allowed by Python.
<li>Computing unique IDs for sections in automatically generated XML or HTML
documents.
<li>Naming page handlers for web server frameworks like CherryPy.
<li>... just use your imagination!
</ul>

The Underscode package is released under the GNU Lesser General Public License
(LGPL) version 3 or later (see [http://www.gnu.org/licenses/]).

<h2>Underscoded strings as attributes</h2>

Underscode provides a module with decorators that allow you to use plain
attribute access as a flexible way of accessing all kinds of "child objects"
without polluting the normal attribute namespace, and with optional
interactive completion if you wish so.  For instance, you can make the
(string) keys of a dictionary accessible as attributes:

<verbatim>
from underscode.decorators import proxy_method

class AttributedDict(dict):
    @proxy_method(dict.__getitem__)
    def __getattr__(self, name):
        return super(AttributedDict, self).__getattr__(name)

    @proxy_method(dict.__setitem__)
    def __setattr__(self, name, value):
        super(AttributedDict, self).__setattr__(name, value)

    @proxy_method(dict.__delitem__)
    def __delattr__(self, name):
        super(AttributedDict, self).__delattr__(name)
</verbatim>

Then, access to an attribute which looks like an underscoded string gets the
name decoded and used as an argument to <code>__getitem__()</code>:

<verbatim>
>>> d = AttributedDict()
>>> d
{}
>>> d.foo = 1
>>> d.foo_ = 42
>>> d.foo_, d['foo'], d.foo
(42, 42, 1)
>>> d
{u'foo': 42}
>>> del d.foo_
>>> d
{}
</verbatim>

Adding tab-completion on underscoded attributes to this simple example is as
easy as applying some ready-to-use decorators on the methods used as arguments
to <code>proxy_method</code>.  See the documentation of
the <code>underscode.decorators</code> module for more information and
examples.

<h2>Python codec API support</h2>

Since the Underscode package is compliant with the standard Python codec
API, you can use Underscode to encode and decode strings with the usual
<code>unicode.encode()</code> and <code>str.decode()</code> calls at any time
just by importing the <code>underscode.codec</code> subpackage (it is not
automatically imported by the main <code>underscode</code> package):

<verbatim>
>>> import underscode.codec
>>> print u'this is \u201ca test\u201d'
this is “a test”
>>> u'this is \u201ca test\u201d'.encode('underscode')
'this__is___u201ca__test_u201d_'
>>> 'this__is___u201ca__test_u201d_'.decode('underscode')
u'this is \u201ca test\u201d'
</verbatim>


<h2>Getting Underscode</h2>

You can download the source code distribution of Underscode from the
Python Package Index at [http://pypi.python.org/].  It uses the standard
<code>setup.py</code> method for installation, runs on any platform and has no
additional dependencies but Python version 2.4 or greater.

You may also be interested in following the development of Underscode; you can
make a clone of its [http://www.fossil-scm.org/|Fossil] repository and
checkout it with::

<verbatim>
$ fossil clone https://elvil.net/fossil/underscode/ underscode.fossil
$ mkdir underscode && cd underscode
$ fossil open ../underscode.fossil
</verbatim>


<h2>Helping Underscode</h2>

It would be great to discuss your opinions and feelings on Underscode in the
group, to know how you used it in your project, and to help solving yours and
others' problems there!  If you come across a bug or you have some enhancement
proposal, you're encouraged to write to the group or create a ticket at
[https://elvil.net/fossil/underscode/]

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