[Tutor] special attributes naming confusion

[Mark Lawrence]

On 06/06/2012 20:19, Dave wrote:
> I was reading some tutorial material on creating iterators. It shows the
> following example implementation of an iterator:
>
> class Reverse:
>      """Iterator for looping over a sequence backwards."""
>      def __init__(self, data):
>          self.data = data
>          self.index = len(data)
>      def __iter__(self):
>          return self
>      def next(self):
>          if self.index == 0:
>              raise StopIteration
>          self.index = self.index - 1
>          return self.data[self.index]
>
>
> My question is how was I supposed to kinow that the function I call using
> the name iter() is implemented using the name __iter__()?
>
> Is there a rule that describes when I would implement an attribute name
> with leading and trailing double underscores, and then call it without
> those underscores? How many names like this exist in Python? Are these
> special cases or is there a general rule that leading and trailing double
> underscores get dropped when calling functions that were implemented with
> these names? I'm trying to understand the big picture as far as how Python
> works when it comes to this situation. Thanks.
>
>
>
>
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Try this to start with 
http://docs.python.org/reference/datamodel.html#special-method-names. 
Note this is for Python 2.7.3, there may be differences in Python 3.x.

-- 
Cheers.

Mark Lawrence.