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I have a custom implementation of dict custom_dict, which overrides and is by-and-large supported by the native Python dict.

  • I override setting (__setitem__) to do some preprocessing to the value, and store it in some proprietary object.
  • When getting(__getitem__), this proprietary object is then converted to a more natural format.

All features when invoked from this custom_dict behave as I like.

The problem is that when you call something like {'a': 1}.update(custom_dict({'b': 2})), the value for 'b' in the updated dict is the proprietary internal storage object, and not the processed value.

How does Python's native dict.update() work? I've overridden all the methods I could think of it using, items, iteritems, values, itervalues, get, and __getitem__, but I haven't seemed to nail any of the ones update() tries to access, which leads me to believe it might be using the c code. Thoughts?

UPDATE: I just found this in the CPython source code:

if (PyDict_Check(b)) {
    ...
}
else {
    /* Do it the generic, slower way */
    ...
}

Perhaps this is a bug, and that should be PyDict_CheckExact(b) as shows up in various other places in the code.

Any idea how to beat this check?

smci
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Kevin Dolan
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  • Do you inherit from `dict`? Maybe not doing so would help. It looks like you don't reuse much of `dict`'s functionality anyway. – 9000 Jan 20 '11 at 20:46
  • Yes, I inherit from dict. Basically all of the methods that I have overridden explicitly call the dict.__ methods after some processing. I figured the alternative of having a supporting dict and using the abstract base class would be worse... – Kevin Dolan Jan 20 '11 at 20:55

0 Answers0