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TypeQuery

Note

Since Python 3.3 there's functools.singledispatch() function which does the similar work in the standard library. We recommend you to use it instead of this.

See also PEP 443.

Build Status

It provides a simple and dirty way to define generic methods to existing types. You can make overloaded methods using this.

Compatibility

TypeQuery does not depend on any non-standard libraries. It works on these environments:

  • Python 2.5 to 3.2
  • CPython, Stackless, PyPy, Jython

Install

Install using pip:

$ pip install TypeQuery

or easy_install:

$ easy_install TypeQuery

Example: JSON encoder

from typequery import GenericMethod
from sys import version_info
from re import sub
from numbers import Real
from collections import Mapping, Iterable

if version_info.major > 2:
    basestring = string = str
else:
    string = unicode

json = GenericMethod('json')

@json.of(type(None))
def json(value):
    return 'null'

@json.of(bool)
def json(value):
    return 'true' if value else 'false'

@json.of(Real)
def json(value):
    return str(value)

@json.of(string)
def json(value):
    def escape(match):
        s = match.group(0)
        if s in ('\\', '"', '\b', '\f', '\n', '\r', '\t'):
            return '\\' + s
        n = ord(s)
        if n < 0x10000:
            return r'\u%04x' % n
        n -= 0x10000
        s1 = 0xd800 | ((n >> 10) & 0x3ff)
        s2 = 0xdc00 | (n & 0x3ff)
        return r'\u%04x\u%04x' % (s1, s2)
    return '"%s"' % sub(r'([\\"]|[^\ -~])', escape, value)

@json.of(Iterable)
def json(value):
    return '[%s]' % ', '.join(json(element) for element in value)

@json.of(Mapping)
def json(value):
    return '{%s}' % ', '.join('%s: %s' % (json(string(key)), json(value))
                              for key, value in value.items())

And defined json function works like:

>>> json(123)
'123'
>>> json(True)
'true'
>>> json({'apple': 3, 'banana': 5, 'carrot': 1})
'{"apple": 3, "banana": 5, "carrot": 1}'

As the above shows, you can define type-aware instance methods to existing types even including ABCs like collections.Iterable.

Author and license

Written by Hong Minhee. Distributed under MIT license. You can find the source code from the Bitbucket repository:

$ hg clone https://bitbucket.org/dahlia/typequery

Changelog

Version 0.1.4

Released on October 18, 2012.

  • Don't use bitbucket-distutils anymore to prevent several headaches related packaging and distribution.

Version 0.1.3

Released on August 29, 2012.

  • Fixed a bug of handling multiple types by one function. [#2]

Version 0.1.2

Released on August 15, 2012.

  • You can inherit existing generic methods using GenericMethod.inherit() method.
  • Added with_receiver option for GenericMethod.of() decorator and Decorator constructor.

Version 0.1.1

Released on May 22, 2012.

  • Now it works well with abstract base classes other than abc.ABCMeta.
  • Fixed a bug of GenericMethod.clone() method. It does not reflect cloned one's changes to the original anymore. [#1]

Version 0.1.0

Released on May 21, 2012.

  • Initial release.

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