xhtml encoding question

[Ulrich Eckhardt]

Am 02.02.2012 12:02, schrieb Peter Otten:
> Ulrich Eckhardt wrote:
>>
>>   >>>  u'abc'.translate({u'a': u'A'})
>> u'abc'
>>
>> I would call this a chance to improve Python. According to the
>> documentation, using a string [as key] is invalid, but it neither raises
>> an exception nor does it do the obvious and accept single-character
>> strings as keys.
>>
>>
>> Thoughts?
>
> How could this raise an exception? You'd either need a typed dictionary (int
> -->  unicode) or translate() would have to verify that all keys are indeed
> integers.

The latter is exactly what I would have done, i.e. scan the dictionary 
for invalid values, in the spirit of not letting errors pass unnoticed.


> The former would go against the grain of Python, the latter would
> make the method less flexible as the set of keys currently need not be
> predefined:
>
>>>> class A(object):
> ...     def __getitem__(self, key):
> ...             return unichr(key).upper()
> ...
>>>> u"alpha".translate(A())
> u'ALPHA'

Working with __getitem__ is a point. I'm not sure if it is reasonable to 
expect this to work though. I'm -0 on that. I could also imagine a 
completely separate path for iterable and non-iterable mappings.


> Using unicode instead of integer keys would be nice but breaks backwards
> compatibility, using both could double the number of dictionary lookups.

Dictionary lookups are constant time and well-optimized, so I'd actually 
go for allowing both and paying that price. I could even imagine 
preprocessing the supplied dictionary while checking for invalid values. 
The result could be a structure that makes use of the fact that Unicode 
codepoints are < 22 bits and that makes the way from the elements of the 
source sequence to the according map entry as short as possible (I'm not 
sure if using codepoints or single-character strings is faster). 
However, those are early optimizations of which I'm not sure if they are 
worth it.

Anyway, thanks for your thoughts, they are always appreciated!

Uli