Subclassing RegexObject

[Peter Otten]

Tobias Weber wrote:

> how do I subclass or at least add a method to something returned by
> re.compile()?

Let's see:

>>> import re
>>> r = re.compile("yadda")
>>> class S(type(r)): pass
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Error when calling the metaclass bases
    type '_sre.SRE_Pattern' is not an acceptable base type

So I'm afraid you can't subclass...

>>> def hello(self): print "hello"
...
>>> type(r).hello = hello
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't set attributes of built-in/extension type 
'_sre.SRE_Pattern'
>>> r.hello = hello
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: '_sre.SRE_Pattern' object has no attribute 'hello'

...nor add a method...

>>> class W(object):
...     def __init__(self, match):
...             self._match = match
...     def __getattr__(self, name):
...             return getattr(self._match, name)
...     hello = hello
...
>>> def my_compile(*args, **kw):
...     m = original_compile(*args, **kw)
...     if m is not None:
...             return W(m)
...
>>> original_compile = re.compile
>>> re.compile = my_compile
>>> re.compile("yadda").hello()
hello

...but alter the meaning of "something returned by re.compile()" you can. 
Now who would want to do that? And why?

Peter