Forbid implicit slice

[thecnoNSMB]

Rule request

Forbid looping constructs over indexes that are equivalent to slice operations.

Thesis

I recently encountered a point in my code where I was using a comprehension to iterate over a range to index into a list. Here is a basic example that currently passes all checks:

my_list = [1, 2, 3, 4, 5]

# Wrong:
my_sublist = [my_list[index] for index in range(1, 4)]

# Right:
my_sublist = my_list[1:4]

A trickier example closer to what I found:

some_text = 'Python!'

an_index = 4

# Wrong (but fails on Jones complexity):
subset = {some_text[index] for index in range(an_index - 1, an_index - 4, -1)}

# Right:
subset = set(some_text[an_index - 3:an_index])

Reasoning

These are redundant, probably slower, and harder to read.

[sobolevn]

The problem is that my_list can possibly not support slice operaions. For example, it can be a dict or QuerySet object, or something else.

I don't think that this rule can be safe without knowing the type of the object. Will be implemented in typed-linter 🌚