Is Python a

In fact, it’s really a case of “buy one, get a bunch free.” Any class that supports forloops automatically supports all iteration contexts in Python, many of which we’veseen in earlier chapters (see Chapter 13 for other iteration contexts). For example,the in membership test, list comprehensions, the map built-in, list and tuple assignments,and type constructors will also call _ _getitem_ _ automatically, if it’s defined:>>> 'p' in X # All call _ _getitem_ _ too1>>> [c for c in X] # List comprehension['S', 'p', 'a', 'm']>>> map(None, X) # map calls['S', 'p', 'a', 'm']>>> (a, b, c, d) = X # Sequence assignments>>> a, c, d('S', 'a', 'm')>>> list(X), tuple(X), ''.join(X)(['S', 'p', 'a', 'm'], ('S', 'p', 'a', 'm'), 'Spam')>>> XIn practice, this technique can be used to create objects that provide a sequenceinterface and to add logic to built-in sequence type operations; we’ll revisit this ideawhen extending built-in types in Chapter 26.User-Defined IteratorsToday, all iteration contexts in Python will try the _ _iter_ _ method first, before trying_ _getitem_ _. That is, they prefer the iteration protocol we learned about inChapter 13 to repeatedly indexing an object; if the object does not support the iterationprotocol, indexing is attempted instead.Technically, iteration contexts work by calling the iter built-in function to try tofind an _ _iter_ _ method, which is expected to return an iterator object. If it’s provided,Python then repeatedly calls this iterator object’s next method to produceitems until a StopIteration exception is raised. If no such _ _iter_ _ method is found,Python falls back on the _ _getitem_ _ scheme, and repeatedly indexes by offsets asbefore, until an IndexError exception is raised.In the new scheme, classes implement user-defined iterators by simply implementingthe iterator protocol introduced in Chapters 13 and 17 (refer back to those chaptersfor more background details on iterators). For example, the following file, iters.py,defines a user-defined iterator class that generates squares:class Squares:def _ _init_ _(self, start, stop):self.value = start - 1self.stop = stop494 | Chapter 24: Class Coding Details# Save state when created