[Python-Dev] __str__ and unicode

[M.-A. Lemburg]

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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