python内置类型的扩展方法

Question

是否可以将扩展方法添加到python内置类型中？我知道我可以通过简单地通过添加新方法来将扩展方法添加到定义的类型。如下：

class myClass:
    pass

myClass.myExtensionMethod = lambda self,x:x * 2
z = myClass()
print z.myExtensionMethod(10)

但是是将扩展方法添加到python内置类型（如列表，字典，…）的任何方法

list.myExtension = lambda self,x:x * 2
list.myExtension(10)

Answer 1

可以使用以下非常聪明的模块在纯Python中完成此操作：

https://pypi.python.org/pypi/forbiddenfruit

例如：

import functools
import ctypes
import __builtin__
import operator

class PyObject(ctypes.Structure):
    pass

Py_ssize_t = hasattr(ctypes.pythonapi, 'Py_InitModule4_64') and ctypes.c_int64 or ctypes.c_int

PyObject._fields_ = [
    ('ob_refcnt', Py_ssize_t),
    ('ob_type', ctypes.POINTER(PyObject)),
]

class SlotsPointer(PyObject):
    _fields_ = [('dict', ctypes.POINTER(PyObject))]

def proxy_builtin(klass):
    name = klass.__name__
    slots = getattr(klass, '__dict__', name)

    pointer = SlotsPointer.from_address(id(slots))
    namespace = {}

    ctypes.pythonapi.PyDict_SetItem(
        ctypes.py_object(namespace),
        ctypes.py_object(name),
        pointer.dict,
    )

    return namespace[name]

def die(message, cls=Exception):
    """
        Raise an exception, allows you to use logical shortcut operators to test for object existence succinctly.

        User.by_name('username') or die('Failed to find user')
    """
    raise cls(message)

def unguido(self, key):
    """
        Attempt to find methods which should really exist on the object instance.
    """
    return functools.partial((getattr(__builtin__, key, None) if hasattr(__builtin__, key) else getattr(operator, key, None)) or die(key, KeyError), self)

class mapper(object):
    def __init__(self, iterator, key):
        self.iterator = iterator
        self.key = key
        self.fn = lambda o: getattr(o, key)

    def __getattribute__(self, key):
        if key in ('iterator', 'fn', 'key'): return object.__getattribute__(self, key)
        return mapper(self, key)

    def __call__(self, *args, **kwargs):
        self.fn = lambda o: (getattr(o, self.key, None) or unguido(o, self.key))(*args, **kwargs)
        return self

    def __iter__(self):
        for value in self.iterator:
            yield self.fn(value)

class foreach(object):
    """
        Creates an output iterator which will apply any functions called on it to every element
        in the input iterator. A kind of chainable version of filter().

        E.g:

        foreach([1, 2, 3]).__add__(2).__str__().replace('3', 'a').upper()

        is equivalent to:

        (str(o + 2).replace('3', 'a').upper() for o in iterator)

        Obviously this is not 'Pythonic'.
    """
    def __init__(self, iterator):
        self.iterator = iterator

    def __getattribute__(self, key):
        if key in ('iterator',): return object.__getattribute__(self, key)
        return mapper(self.iterator, key)

    def __iter__(self):
        for value in self.iterator:
            yield value

proxy_builtin(list)['foreach'] = property(foreach)

import string

print string.join([1, 2, 3].foreach.add(2).str().add(' cookies').upper(), ', ')

>>> 3 COOKIES, 4 COOKIES, 5 COOKIES

在那里，感觉不舒服吗？