__str__ vs. __repr__

[David Gobbi]

Gerrit Holl <gerrit.holl at pobox.com> wrote:
> Randall Hopper wrote:
>> 
>> 1) Is there a convention for what __str__ and __repr__ should return for
>>    classes?

> __str__ should return a string, __repr__ may also return, for example, a
> dictionairy.

The Python Language Reference Manual has a few lines on this subject,
specifically in Section 3.3.1.  

__repr__ (self) 
       Called by the repr() built-in function and by string conversions 
       (reverse quotes) to compute the "official" string representation 
       of an object. This should normally look like a valid Python
       expression that can be used to recreate an object with the same 
       value. By convention, objects which cannot be trivially converted 
       to strings which can be used to create a similar object produce a
       string of the form "<...some useful description...>". 

__str__ (self) 
       Called by the str() built-in function and by the print statement 
       to compute the "informal" string representation of an object. 
       This differs from __repr__() in that it does not have to be a valid
       Python expression: a more convenient or concise representation may 
       be used instead. 

In short:  no they are not the same, yes you can define them both.  If you
           don't define __str__(), then str(object) will default to
           repr(object)

  - David
>> 2) Or, whatever they return, should they return the same value?

> I don't know: I think it's wrong to use both.

> regards,
> Gerrit.
> -- 
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-- 
--David Gobbi, MSc                    dgobbi at irus.rri.on.ca
  Advanced Imaging Research Group
  Robarts Research Institute, University of Western Ontario