Question

是否可以为python内置类型添加扩展方法？我知道我可以通过简单地添加新方法来将扩展方法添加到已定义的类型。如下：

class myClass:
    pass

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

但是有任何方法可以将扩展方法添加到python built'in类型，如list，dict，...

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

Answer 1

可以使用这个非常聪明的模块在纯Python中完成：

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

那里，感觉不是很好吗？

Answer 2

没有。 C中定义的类型不能进行monkeypatched。

Answer 3

不，你必须是子类！

>>> import string
>>> class MyString(str):
...     def disemvowel(self):
...         return MyString(string.translate(self, None, "aeiou"))
... 
>>> s = MyString("this is only a test")
>>> s.disemvowel()
'ths s nly  tst'

或者更具体到您的示例

>>> class MyList(list):
...     pass
... 
>>> MyList.myExtension = lambda self,x:x * 2
>>> l = MyList()
>>> l.myExtension(10)
20

Answer 4

不，因为我很确定所有内置类型都是用优化的C编写的，因此不能用Python修改。当我尝试它时，我得到：

TypeError: can't set attributes of built-in/extension type 'list'

Answer 5

您可以做的最好的事情似乎是从内置类型派生一个类。例如：

class mylist(list):
    def myfunc(self, x):
        self.append(x)

test = mylist([1,2,3,4])
test.myfunc(99)

（你甚至可以将它命名为“list”，以便获得相同的构造函数，如果你愿意的话。）但是，你不能像问题中的例子一样直接修改内置类型。

python内置类型的扩展方法！

5 个答案: