On Thu, 03 Sep 2009 15:46:01 -0700, Ken Newton wrote:
> I have created the following class definition with the idea of making a
> clean syntax for non-programmers to created structured data within a
> python environment.
What do you expect non-programmers to do with this class, without
programming? How can they even use it?
...
> The expected use would have all items in the structure be simple python
> types or AttrClass types. Code written in python could walk the
> structure in a simple way to locate any desired values. Code in a C/C++
> extension should also be able to walk the structure to use any value in
> the structure.
I don't see the purpose of it. Nested data structures are generally
harder for people to understand than non-nested ones, hence the Python
Zen: "flat is better than nested". For example, a list is easier to grasp
than a tree. This especially applies to non-programmers.
I don't see how this is simple enough for non-programmers, or useful for
programmers. For programmers, just nest objects:
class Parrot(object):
pass
obj = Parrot()
obj.x = 1
obj.y = Parrot()
obj.y.z = 2
obj.y.z.zz = Parrot()
> class AttrClass(object):
> """AttrClass lets you freely add attributes in nested manner"""
You don't actually need a special class for that, unless you're providing
extra functionality. A bare subclass of object will let you freely add
attributes in a nested manner.
It seems to me that you're combining two different sets of functionality,
but only describing one. The first is, nested attributes -- but you get
that for free with any class. The second is the ability to set (but
strangely not retrieve!) attributes using dictionary-like syntax. But
that's implied by the code, you haven't mentioned it in your description
or documentation.
> def __init__(self):
> pass
If the __init__ method doesn't do anything, you don't need it.
> def __setitem__(self, key, value):
> return self.__dict__.__setitem__(key, value)
Simpler to just say:
def __setitem__(self, key, value):
self.__dict__[key] = value
You don't strictly need the return, because methods return None by
default, and dict.__setitem__ always returns None (unless it raises an
exception).
This method allows you to set attributes using dict syntax:
instance['key'] = 123 # same as instance.key = 123
But you don't have corresponding __getitem__ or __delitem__ methods, so
you can't do these:
value = instance['key'] # fails
del instance['key'] # fails
> def __repr__(self):
> return "%s(%s)" % (self.__class__.__name__,
> self.__dict__.__repr__())
This strongly implies that you should be able to create a new instance
using that format:
AttrClass({'key': 123, 'another_key': 456})
but that fails. As a general rule, the repr() of a class should (if
possible) work correctly if passed to eval(). This doesn't. That's not
entirely wrong, but it is unusual and confusing.
--
Steven
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