how to create nested classes dynamically

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how to create nested classes dynamically

by gopal mishra :: Rate this Message:

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I have class structure as below. How can I create the following nested class and its properties dynamically.

class AA(object):

class BB(object):

def setBB1(self, value):

##some code

def getBB1(self):

bb1 = #somecode

return bb1

bb1 = property(getBB1, setBB1, None, None)

bb2 = ...

bb = BB()

class CC(object):

....

cc = CC()

aa = AA()

print aa.bb.bb1

aa.bb.bb2 = ‘10’

print aa.bb.bb2

I want to achive dot structure get or set value.i.e. aa.bb.bb1

Thanks,

Gopal

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Re: how to create nested classes dynamically

by Gabriel Genellina-7 :: Rate this Message:

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En Wed, 04 Nov 2009 02:04:11 -0300, gopal mishra <gopalm@...>
escribió:

> I have class structure as below. How can I create the following nested
> class
> and its properties dynamically.
>
>
> class AA(object):
>
> class BB(object):
>
> def setBB1(self, value):
>
> ##some code
>
> def getBB1(self):
>
> bb1 = #somecode
>
> return bb1
>
> bb1 = property(getBB1, setBB1, None, None)
>
> bb2 = ...
>
> bb = BB()
>
> class CC(object):
>
> ....
>
> cc = CC()
>
> aa = AA()

First, I assume getBB1 and setBB1 really do some actual work. If they're
just accessors for an instance attribute, don't use them; don't write Java
in Python [1]

In Python, you may have instance (or "normal") attributes, and class
attributes. When you say obj.name, if name is not found as an instance
attribute, it is looked up on its class (and all its base classes; this is
how methods are searched, BTW)
Class attributes are "shared" among all instances - that is, all instances
retrieve the same object when you access a class attribute.

Your code above, as it is written, creates two class attributes named bb
and cc (they're class attributes because the statements bb=... and cc=...
are inside the class definition). It works, but perhaps that's not what
you want. If you want instance attributes instead, create them in
AA.__init__ by using self.bb=something

Nested classes provide no benefit here and are harder to use, so just move
the class definitions to the module level. The code would become:

class BB(object):
def setBB1(self, value):
##some code

def getBB1(self):
"docstring for the property"
bb1 = #somecode
return bb1

bb1 = property(getBB1, setBB1)
bb2 = ...

class CC(object):
....

class AA(object):
def __init__(self, ...):
self.bb = BB()
self.cc = CC()

Then, you can write:

aa = AA()
print aa.bb.bb1
aa.bb.bb2 = '10'
print aa.bb.bb2

[1] http://dirtsimple.org/2004/12/python-is-not-java.html

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Gabriel Genellina

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