From: "Guido van Rossum" <guido@python.org>
> I'm not sure what you are asking about, but let me give an example.
> You can write an auxiliary class that "describes" an instance
> attribute. Instances of this "descriptor" class are stored in a class
> dict. The descriptor class implements a method __get__ which is
> called in two situations:
>
> (a) when a class attribute is retrieved, <attr>.__get__(None, <class>)
> is called; this can return an unbound method
>
> (b) when an instance attribute is retrieved, <attr>.__get__(<inst>, <class)
> is called; this can return a bound method
>
> Does this help?
>
Yes, thanks. Exactly what I meant. You only forgot to mention that
the descriptor class must derive from object: is this intended?
I needed this to write
class X:
method = myinstancemethod(func)
instead of
class X:
pass
X.method = new.instancemethod(func, None, X)
where myinstancemethod is the descriptor class, and func
is any callable object (maybe a function implemented in C).
Two additional comments:
- Shouldn't (my)instancemethod be a builtin? Similar to
staticmethod and classmethod?
- The following seems to be a bug (remember, I'm on Windows):
C:\>c:\python22\python.exe
Python 2.2a2 (#22, Aug 22 2001, 01:24:03) [MSC 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> class myinstancemethod(object):
... def __init__(self, func):
... self.func = func
... def __get__(self, inst, klass=None):
... import new
... return new.instancemethod(self.func, inst, klass)
...
>>> class X:
... meth = myinstancemethod(lambda *x: x)
...
>>> X().meth
<bound method X.<lambda> of <__main__.X instance at 007C7F04>>
>>> X().meth()
(<__main__.X instance at 007E80E4>,)
>>> X.meth
Traceback (most recent call last):
File "<stdin>", line 1, in ?
SystemError: NULL object passed to Py_BuildValue
Thomas
RetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4