Does Python have extension methods like C#? Is it possible to call a method like:
MyRandomMethod()
on existing types like int
?
not sure if that what you're asking but you can extend existing types and then call whatever you like on the new thing:
class int(int):
def random_method(self):
return 4 # guaranteed to be random
v = int(5) # you'll have to instantiate all you variables like this
v.random_method()
class int(int):
def xkcd(self):
import antigravity
print(42)
>>>v.xkcd()
Traceback (most recent call last):
File "<pyshell#81>", line 1, in <module>
v.xkcd()
AttributeError: 'int' object has no attribute 'xkcd'
c = int(1)
>>> c.random_method()
4
>>> c.xkcd()
42
hope that clarifies your question
I've had great luck with the method described here:
http://mail.python.org/pipermail/python-dev/2008-January/076194.html
I have no idea if it works on builtins though.
Another option is to override the meta-class. This allows you to, among other things, specify functions that should exist in all classes.
This article starts to discuss it:
http://www.onlamp.com/pub/a/python/2003/04/17/metaclasses.html
The following context manager adds the method like Forbidden Fruit would without the limitations of it. Besides that it has the additional benefit of removing the extension method afterwards:
class extension_method:
def __init__(self, obj, method):
method_name = method.__name__
setattr(obj, method_name, method)
self.obj = obj
self.method_name = method_name
def __enter__(self):
return self.obj
def __exit__(self, type, value, traceback):
# remove this if you want to keep the extension method after context exit
delattr(self.obj, self.method_name)
Usage is as follows:
class C:
pass
def get_class_name(self):
return self.__class__.__name__
with extension_method(C, get_class_name):
assert hasattr(C, 'get_class_name') # the method is added to C
c = C()
print(c.get_class_name()) # prints 'C'
assert not hasattr(C, 'get_class_name') # the method is gone from C
You can add whatever methods you like on class objects defined in Python code (AKA monkey patching):
>>> class A(object):
>>> pass
>>> def stuff(self):
>>> print self
>>> A.test = stuff
>>> A().test()
This does not work on builtin types, because their __dict__
is not writable (it's a dictproxy
).
So no, there is no "real" extension method mechanism in Python.
It can be done with Forbidden Fruit (https://pypi.python.org/pypi/forbiddenfruit)
Install forbiddenfruit:
pip install forbiddenfruit
Then you can extend built-in types:
>>> from forbiddenfruit import curse
>>> def percent(self, delta):
... return self * (1 + delta / 100)
>>> curse(float, 'percent', percent)
>>> 1.0.percent(5)
1.05
Forbidden Fruit is fundamentally dependent on the C API, it works only on cpython implementations and won’t work on other python implementations, such as Jython, pypy, etc.