Why is the range not exhausted in Python-3?

Question

If I do the following:

a = range(9) for i in a: print(i) # Must be exhausted by now for i in a: print(i) # It starts over! 

Python generators after raising StopIteration usually stop the loop. How then does the range produce this pattern - it restarts after each iteration.

Answer 1

As others have said, range not a generator, but has a sequence type (like a list) that makes it iterable , which does NOT match the iterator .

The differences between iterable , iterator and generator are subtle (at least for someone new to python).

• An iterator provides the __next__ method and can be exhausted, thereby raising StopIteration .
• An iterable is an object that provides an iterator according to its contents. Whenever its __iter__ method __iter__ called, it returns a NEW iterator object, so you can (indirectly) iterate over it several times.

• A generator is a function that returns an iterator that can be exhausted.

• It is also useful to know that the for loop automatically queries the iterator any iterable . That is why you can write for x in iterable: pass instead of for x in iterable.__iter__(): pass or for x in iter(iterable): pass .

All this is in the documentation, but IMHO is somewhat difficult to find. The best starting point is probably Glossary .

Answer 2

range is a kind of immutable sequence type. The iteration does not exhaust it.

 >>> a = iter(range(9)) # explicitly convert to iterator >>> >>> for i in a: ... print(i) ... 0 1 2 3 4 5 6 7 8 >>> for i in a: ... print(i) ... >>> 

Answer 3

range not a generator; it is a type of sequence , such as strings or lists .

So

 for i in range(4): 

no different from

 for i in "abcd":