[Python-Dev] Dicts are broken Was: unicode hell/mixing str and unicode asdictionarykeys

[Michael Hudson]

Michael Chermside <mcherm at mcherm.com> writes:

> I'm changing the subject line because I want to convince everyone that
> the problem being discussed in the "unicode hell" thread has nothing
> to do with unicode and strings. It's all about dicts.

I'd say it's more to do with __eq__.  It's a strange __eq__ method
that raises an Exception, IMHO.

Please do realize that the motivation for this change was hours and
hours of tortous debugging caused by a buggy __eq__ method making keys
"impossibly" seem to not be in dictionaries.

> I have not observed real breakage in my own code, but I will present
> a sample of made-up-but-completely-reasonable code that works in
> 2.4, fails in 2.5, and arguably ought to work fine. I think we should
> restore the behavior of dicts that when they compare keys for
> equality they suppress exceptions (treating the objects as unequal),
> or at LEAST retain the behavior for one more release making it a
> warning this time.

Please no.  Here's just one piece of evidence that the 2.4 semantics
are pretty silly too:

>>> d = {u'\xe0':1, '\xe0\:2}
  File "<stdin>", line 1
    d = {u'\xe0':1, '\xe0\:2}
                            ^
SyntaxError: EOL while scanning single-quoted string
>>> d = {u'\xe0':1, '\xe0':2}
>>> '\xe0' in d
True
>>> '\xe0' in d.keys()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe0 in position 0: ordinal not in range(128)

Cheers,
mwh

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