[SIM904][False-positive] Accessing previous dict values

[Skylion007]

Desired change

• Rule(s): SIM986, SIM987
• Adjustment: In which way should it/they be adjusted?

Explanation

• The SIM904 check currently does not check if previous values were accessed in keys. This means new keys cannot access old keys since the dictionary is not yet constructed.

Why is the adjustment necessary / better?

Example

This is an example where the mentioned rule(s) would currently be suboptimal:

        perf = {"total_time": end_time - start_time}
        perf["frame_time"] = perf["total_time"] / total_frames
        perf["fps"] = 1.0 / perf["frame_time"]
        perf["time_per_step"] = time_per_step
        perf["avg_sim_step_time"] = total_sim_step_time / total_frames

or more simply:

        perf = {"a": 1}
        perf["b"] = perf["a"] / 10

Yes, in this case, it could be written by creating lots of additional variables to replace the references to previous values of "total_time" and "frame_time", but in more complicated dictionaries it seems like this rule could become more troublesome,

[MartinThoma]

Good catch, I'll fix that tomorrow.

[MartinThoma]

Just in case you missed it : in order to still add new rules quickly and don't disturb users of flake8-simplify, I'll use SIM9 rules. If there are no more false positives for 6 months, I'll change the rule to something not beginning with "9". This way people can ignore the SIM9 rules in their CI and just try them once in a while.

[MartinThoma]

This looks very similar to #99 . I'll address both in the same PR/commit