Tidy local imports (PyInf#11558)

[ArvidJB]

Currently tidy-imports only optimizes global imports. How difficult would it be to also optimize "local" imports, i.e., imports within a function? Example:

$ cat foo.py
import os

def foo():
    import os
    import sys
    return os.getenv('FOO')
$ tidy-imports foo.py
[PYFLYBY] /tmp/foo.py: removed unused 'import os'
[PYFLYBY] /tmp/foo.py: added mandatory 'from __future__ import annotations'
--- /tmp/foo.py   2023-11-21 16:37:32.473138334 -0500
+++ /tmp/tmpgciyp7p6    2023-11-21 16:38:48.351697332 -0500
@@ -1,4 +1,5 @@
-import os
+from __future__ import annotations
+

 def foo():
     import os

Replace /tmp/foo.py? [y/N]

Here we should

1. detect that import sys is unused in foo and suggest to remove it
2. detect that import os is present both at global as well as local scope. I think here it's correct to remove the global import since the only usage is in a function where os is imported locally. But in general if there's a global import not covered by local imports everywhere we should remove the local import.

Can you estimate how much work this would be?

[Carreau]

I've been asked to come back to this.

My feeling with the architecture of pyflyby is that it's going to be complex, and just estimating the work would need significant work to figure out what is needed.

I'll try to look into in over the next few weeks to see what I can do, and try to come up with a plan/estimate.

[ArvidJB]

Hi @Carreau, do you have an estimate how much work this would be?

[Carreau]

I haven't been able to look into it, I'm trying to get the pyinstruments fixes first. I'll put that higher on the priority list.