Retrieve length of slice from slice object in Python

Question

The title explains itself, how to get 2 out of the object

slice(0,2)

The documentation is somewhat confusing, or it is the wrong one

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Answer 1

a simplified approach with asserts

The length depends on the target object, which is sliced. But one can define a maximum length.

Example

define your maximum length function like this

def slice_len_max(s):
    assert (s.start is not None)
    assert (s.stop is not None)
    step = 1
    if s.step is not None:
        step = s.step
    return max((s.stop - s.start) // step, 1)

and check the output

>>> slice_len_max(slice(0, 10))
10
>>> slice_len_max(slice(0, 10, 2))
5
>>> slice_len_max(slice(0, 10, 3))
3
>>> slice_len_max(slice(0, 10, 10))
1
>>> slice_len_max(slice(0, 10, 100))
1
>>> slice_len_max(slice(3))
Traceback (most recent call last):
  File "", line 1, in 
  File "", line 2, in slice_len_max
AssertionError

The last call crashes, as the slice has no start attribute defined.