> map calls, list comprehension, etc. For loops, etc. > work by indexing a sequences from zero to a higher > index until out-of-bounds is reached.
What makes you think that? So far as I know for loops work by calling next on an iterator until nothing gets returned, no indexes involved.(At least not in the for loop) But they could just as well work by calling the len() function and iterating that number of times. And len() could be stored as part of the data structure ala Pascal arrays. The point being that it is dangerous to assume how a language feature works internally, it can change from version to version. In this case the iterator solution means that the for loop can work on any iterable entity - like files for instance. > But why does this work? > >>>> class stepper: > ... def __getitem__(self, i): > ... return self.data[i] > ... >>>> 'p' in X > True > > What does 'in' have to do with indexing? Nothing unless its implementation uses a while loop and index, but thats unlikely. But your code doesn't show what X is, I assume its an instance of stepper? (The convention is for uppercase class names and lower case object names so I'm slightly unsure about that assumption!) But we don't even have the whole of stepper since there is no self.data definition. Its kind of hard to say. I'm slightly confused by the question, sorry. Alan G Author of the learn to program web tutor http://www.freenetpages.co.uk/hp/alan.gauld _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
