How to iterate over a slice?

Question

A slice in python is not iterable. This code:

s = slice(1, 10, 2)
iter(s)

results in this error:

TypeError: 'slice' object is not iterable

This is the code I've come up with to show the slice by creating a list iterable:

list(range(s.start, s.stop, s.step))

This uses the start, stop and step attributes of the slice object. I plug those into a range (an immutable sequence type) and create a list:

[1, 3, 5, 7, 9]

Is there something missing? Can I iterate over a slice any better?

Answer 1

A slice isn't an iterable. It doesn't contain elements, but instead specifies which elements in some other iterable are to be returned if the slice is applied to that iterable.

Since it's not an iterable, you can't iterate over it. As you have discovered, however, you can obtain the indices for which it will return elements from an iterable to which it is applied, using range() - and you can iterate over that:

s = slice(1, 10, 2)
indices = range(s.start, s.stop, s.step)
it = iter(indices)

>>> list(it)
[1, 3, 5, 7, 9]