[英]Extension method for python built-in types
是否可以將擴展方法添加到 python 內置類型? 我知道我可以通過簡單地添加新方法來將擴展方法添加到定義的類型。 如下:
class myClass:
pass
myClass.myExtensionMethod = lambda self,x:x * 2
z = myClass()
print z.myExtensionMethod(10)
但是有什么方法可以將擴展方法添加到 python 內置類型,如列表、字典、...
list.myExtension = lambda self,x:x * 2
list.myExtension(10)
它可以用這個非常聰明的模塊在純 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
在那里,感覺不是很好嗎?
不可以。 C 中定義的類型不能進行猴子補丁。
不,你必須子類!
>>> 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'
或更具體到您的示例
>>> class MyList(list):
... pass
...
>>> MyList.myExtension = lambda self,x:x * 2
>>> l = MyList()
>>> l.myExtension(10)
20
不,因為我很確定所有內置類型都是用優化的 C 編寫的,因此不能用 Python 進行修改。 當我嘗試它時,我得到:
TypeError: can't set attributes of built-in/extension type 'list'
你能做的最好的似乎是從內置類型派生一個 class 。 例如:
class mylist(list):
def myfunc(self, x):
self.append(x)
test = mylist([1,2,3,4])
test.myfunc(99)
(如果需要,您甚至可以將其命名為“list”以獲得相同的構造函數。)但是,您不能像問題中的示例那樣直接修改內置類型。
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