Recursive Str?

Steven Bethard steven.bethard at gmail.com
Fri Oct 22 09:01:41 CEST 2004


Chris S. <chrisks <at> NOSPAM.udel.edu> writes:

> 
> Why do most, if not all, compound Python structures not convert their 
> elements to strings recursively?
> 
>  >>> class foo:
> ...     def __init__(self, a):
> ...         self.a = a
> ...     def __str__(self):
> ...         return 'foo('+str(self.a)+')'
> ...
>  >>> from sets import Set
>  >>> a=Set([foo(1)])
>  >>> print a
> Set([<__main__.foo instance at 0x01C01968>])

Well, they call the __repr__ method, not the __str__ method:

>>> class foo:
...     def __init__(self, a):
...         self.a = a
...     def __str__(self):
...         return 'foo(%s)' % self.a
...
>>> set([foo(1)])
set([<__main__.foo instance at 0x009D8030>])
>>> class foo:
...     def __init__(self, a):
...         self.a = a
...     def __repr__(self):
...         return 'foo(%s)' % self.a
...
>>> set([foo(1)])
set([foo(1)])

Were you just looking for this behavior, or were you asking why it's __repr__ 
and not __str__?

Steve




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