[Python-Dev] __str__ and unicode
M.-A. Lemburg
mal at egenix.com
Wed Dec 6 10:51:27 CET 2006
On 2006-12-06 10:46, M.-A. Lemburg wrote:
> On 2006-12-06 10:26, Fredrik Lundh wrote:
>> over at my work copy of the python language reference, Adrian Holovaty
>> asked about the exact semantics of the __str__ hook:
>>
>> http://effbot.org/pyref/__str__
>>
>> "The return value must be a string object." Does this mean it can be a
>> *Unicode* string object? This distinction is ambiguous to me because
>> unicode objects and string objects are both subclasses of basestring.
>> May a __str__() return a Unicode object?
>>
>> I seem to remember earlier discussions on this topic, but don't recall when
>> and what. From what I can tell, __str__ may return a Unicode object, but
>> only if can be converted to an 8-bit string using the default encoding. Is this
>> on purpose or by accident? Do we have a plan for improving the situation
>> in future 2.X releases ?
>
> This was added to make the transition to all Unicode in 3k easier:
>
> .__str__() may return a string or Unicode object.
>
> .__unicode__() must return a Unicode object.
>
> There is no restriction on the content of the Unicode string
> for .__str__().
One more thing, since these two hooks are commonly used with str() and
unicode():
* unicode(obj) will first try .__unicode() and then revert to .__str__()
(possibly converting the string return value to Unicode)
* str(obj) will try .__str__() only (possibly converting the Unicode
return value to a string using the default encoding)
--
Marc-Andre Lemburg
eGenix.com
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