A couple of OOPython questions
Alexy Khrabrov
braver at pobox.com
Tue Sep 9 12:12:39 EDT 2003
Reading python books feels a bit like reading Perl books -- although
OO is there, some fundamental questions are not illuminated, and then
OO comes after scripting or text, as in the Cookbook! E.g., a = b is
a deep copy. How do you do shallow copy? What are the equivalent of
copy constructors?
Here's another OO question for some real-life application, not that
puny regex fun (or was that perl? :)... I've developed a CORBA server
for structural protein data, and made a simple python client for it
with omniORBpy. My server wraps a huge DB2 database into a series of
accessors, each returning rows from the corresponding table. Let's
say I just want to view the rows. As I came to expect, the thing
(perl or python) will unravel and pretty-print any hierarchy of
dictionaries or lists. [I can't help it, but perl books are shorter
since hash is a better term than a dictionary! Just like with graphs,
where node saves you space over vertex.]
OK, now I go to my python prompt and I want to inspect my objects as
returned by the CORBA server. One of them represents an atom site. I
merrily type just its name to see the great unknown unwrap before my
eyes. Here:
>>> a
<MMS.StructConf instance at 0x8cb1b44>
Hmm. That's not what I hoped for. Some fragments of code I saw run
through my mind and I type in,
>>> dir(a)
['_NP_RepositoryId', '__doc__', '__init__', '__module__', 'beg_auth',
'beg_label', 'conf_type', 'details', 'end_auth', 'end_label', 'id']
Good, we're getting somewhere. I also googled out vars(a), which
seems to be the same as a.__dict__ (are they?... why is __dict__ not
shown above then? 2.2...)
Printing out gazillion fields by hand for each class is silly, they
only wrap strings and numbers and other objects of that nature. I am
ready to dive in a recursive descent. No such luck -- whoever created
CORBA bindings for python didn't make those objects dictionary-like!
I can't get members by name, although they _are_ in some __dict__,
useless apparently, until I supply __getitem__!
Is there an easy way to write something _once_, general enough, to
print out a hierarchy of nested objects which just don't have
__getitem__, although every field is either a string or a number or
another object?
Cheers,
Alexy Khrabrov
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