[Python] Nested class structures

For a variety of reasons, I'm interested in putting together some
code that will allow me to created structures out of nested classes,
something like:

class class1:
def methA(self):
print "Some code here"
class class2:
propA = "A"
def methB(self):
print "Some more code here"
class class3:
# etc.
class class4:
pass
#etc

The main problem is that Python does not seem to provide enough
information about the lexical context of definitions like this. In
particular, I would like the ability to have some of the nested classes
be "anonymous" -- that is, I don't want to have to worry about choosing
identifiers for them. I'd LIKE to do this:

class class1:
class anon: pass
class anon: pass
class anon: pass

. . . and somehow intercept or monitor the name-binding that's
going on there so I wind up with three separate classes which are bound
to uniquely named attributes of class1. But I can't do this because
each anon stomps on the previous name binding, and there doesn't seem to
be a way to intervene and bind a new attribute in class1, because class1
isn't really created until after all the nested class definitions
happen.

I've been playing around with various metaclass approaches, but I
can't seem to get it to really work. (In the nested class structures,
the metaclass instantiations happen from the bottom up, and that's the
main snag.) Are there any hooks or hacks that would allow me to affect
the way nested class definitions are bound to the attribute names of an
enclosing class definition? Or alternatively, a way to construct on the
fly a separate list or tree that reflects the nesting structure?

--
--OKB (not okblacke)
Brendan Barnwell
"Do not follow where the path may lead. Go, instead, where there is
no path, and leave a trail."
--author unknown

Larry Bates wrote:

It is a little hard to understand what you want but you
may just want to put class instances in a list.

class anon:
pass

class class1:
def __init__(self):
self.l=[anon(), anon(), anon()]

This is why I want to define the classes inline, nested in the
other class. I'm trying to leverage the syntactic structure of class
definitions to get nested structures of code. It's somewhat akin to

a = { 'one': 1,
'nested': { 'two': 2, 'three': 3,
'nestnest': { 'four': 4, 'five': 5 }
}
'othernest': { 'six': 6 }
}

. . . except that I want the ability to include arbitrary python
code where I have 1, 2, 3 there (as dictionary values). As far as
I can tell, Python doesn't provide a way to define code as part of
a larger expression like this, except in a class definition.

You can capture before redefining without any need to exec:
... anons=[]
... class anon:
... def method1(self): return 'the first'
... anons.append(anon)
... class anon:
... def method1(self): return 'the second'
... anons.append(anon)
... class anon:
... def method1(self): return 'the third'
... anons.append(anon)
... del anon

... anons=[]
... class anon:
... def method1(self): return 'the first'
... anons.append(anon)
... class anon:
... def method1(self): return 'the second'
... anons.append(anon)
... class anon:
... def method1(self): return 'the third'
... anons.append(anon)
... del anon
...
...
the first
the second
the third
That is indeed totally mysterious to me. I have a decent grasp of
what can be done, but sometimes the deeper question of why anybody
might ever possibly want to do it escapes me totally, and this is
such a case.

On Sat, Sep 11, 2004 at 12:28:44AM +0000, OKB (not okblacke) wrote:
Yeah, sorry, I should have been a little more clear. Anyway, it's
important that these be actual class definitions, because I want the
ability to include per-class methods and stuff. So I don't really want
a bunch of identical anonymous classes. I want something like:

class class1:
class anon:
def meth1(self): print "meth1"
class anon:
def meth1(self): print "different meth1"
class anon:
def meth1(self): print "another meth1"

This is why I want to define the classes inline, nested in the
other class. I'm trying to leverage the syntactic structure of class
definitions to get nested structures of code. It's somewhat akin to

a = { 'one': 1,
'nested': { 'two': 2, 'three': 3,
'nestnest': { 'four': 4, 'five': 5 }
}
'othernest': { 'six': 6 }
}

. . . except that I want the ability to include arbitrary python
code where I have 1, 2, 3 there (as dictionary values). As far as
I can tell, Python doesn't provide a way to define code as part of
a larger expression like this, except in a class definition.