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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Custom string joining
Date: Mon, 09 May 2011 19:16:24 -0400
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:5038

On 5/9/2011 4:25 PM, Claudiu Popa wrote:

> I  already told in the first post that I've implemented __str__ function,
 > but it doesn't seems to be automatically called.

No, Python does not auto-coerce to strings (only between numbers).
You have to be explicit by calling str. Karim's statement "You just have 
to implement __str__() python special method for your "custom_objects". 
" means that str will then work.

> For instance, the following example won't work:
>
>>>> class a:
>          def __init__(self, i):
>                  self.i = i
>          def __str__(self):
>                  return "magic_function_{}".format(self.i)
>>>> t = a(0)
>>>> str(t)
> 'magic_function_0'
>>>> "".join([t])

print('\n'.join(str(ob) for ob in [a(0), a(1), a(None)]))

magic_function_0
magic_function_1
magic_function_None

-- 
Terry Jan Reedy