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A simple and dirty way to define generic methods to existing types.

Project description


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.


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

  • Python 2.5–2.7, 3.2–3.5
  • CPython, Stackless, PyPy, Jython


Install using pip:

$ pip 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
    string = unicode

json = GenericMethod('json')

def json(value):
    return 'null'

def json(value):
    return 'true' if value else 'false'

def json(value):
    return str(value)

def json(value):
    def escape(match):
        s =
        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)

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

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)
>>> json(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


Version 0.1.5

Released on June 23, 2016.

  • Compatibility with recent Python versions: Python 3.3 to 3.5, and PyPy3.

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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