complicated class question

[sismex01 at hebmex.com]

> From: Alex Martelli [mailto:aleax at aleax.it]
> 
> Fred Clift wrote:
>    ...
> > class a:
> >     def foo(self):
> >         print "hi"
> > 
> > 
> > class b:
> >     def bar(self):
> >         ainst = a()
> >         ainst.foo()
> > 
> > 
> > say that a is defined in a system library and that b is in 
> > a 3rd party library.
> 
> Then presumably you have, in thirdparty.py:
> 
> import syslib
> class b:
>     def bar(self):
>         ainst = syslib.a()
>         ainst.foo()
> 
> right?  So basically all you need to ensure before you import 
> thirdparty that ITS import of syslib will get YOUR tweaked version
> of module syslib, and there you are.
> 
> So for example you'll have in mysyslib.py:
> 
> import syslib as true_syslib
> class a(true_syslib.a):
>     def foo(self):
>         print 'bye'
> 
> 
> > I'd like to get b to use a modified version a, without 
> > having to change the code of either
> > 
> > 
> > my code would do something like:
> > 
> > binst = b()
> > <insert your solution here>
> > binst.bar()
> 
> You want to intervene too late, I think.  BEFORE you import 
> thirdparty, you'll have to install your tweaked mysyslib module
> as syslib.  So:
> 
> import sys
> import mysyslib
> sys.modules['syslib'] = mysyslib
> import thirdparty
> binst = thirdparty.b()
> binst.bar()
>

But in this case, aren't you substituting the whole syslib
with your own module, instead of only the definition that
the OP wishes to change?

I thought that 'syslib.a' was only looked up when an instance
of 'thirdparty.b' was created.  Opinion Alex?

-gustavo