Does Python have extension methods like C#? Is it possible to call a method like:
MyRandomMethod()
on existing types like int?
myInt.MyRandomMethod()
views:
446answers:
4
+4
A:
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
SilentGhost
2009-02-05 00:53:57
But I mean calling directly on existing types, not MyInt, but int. So like v = 5; v.RandomMethod();
Joan Venge
2009-02-05 01:07:37
you can call class int(int), but you'd need to instantiate variable like: v= int(5)
SilentGhost
2009-02-05 01:10:47
Nice XKCD reference.
Evan Fosmark
2009-02-05 02:32:43
Thanks. So in effect this class can be written several times with different methods and int will get all of these?
Joan Venge
2009-02-05 17:15:46
If you make multiple definitions like this, each one will inherit from the previous one, and so additional methods will accumulate in the most recently-defined "int" class. But the classes defined along the way don't change (tho you lose your reference to them), nor do previously-created instances.
Carl Meyer
2009-02-05 18:02:00
NB: this is almost always a bad thing to do in real Python code. Unlike with extension methods in C#, here you are actually making the variable "int" refer to a completely different (inherited) class, which violates the principle of least surprise (i.e. suddenly isinstance(5, int) is False - WTF?)
Carl Meyer
2009-02-05 18:04:33
+6
A:
You can add whatever methods you like on class objects defined in Python code (AKA monkey patching):
>>> class A(object):
>>> pass
>>> def test(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.
Torsten Marek
2009-02-05 00:59:31
A:
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
tsellon
2009-02-05 01:14:45
+1
A:
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.
hernan43
2009-02-05 17:59:17