False positive "returns `o` but `o` may be unbound on some paths"

error[names_unbound]: Function `occ` returns `o` but `o` may be unbound on some paths
  --> taxonomy/shell.py:2169:12
       |
2169 |     return o
       |            ^
       |
   = help: Assign `o` unconditionally before the `return`, or add a default value
   = note: Basilisk detects variables that are assigned only inside conditional branches (if/while/try) and may not be defined on every execution path
   = see: https://www.basilisk-python.dev/errors/names_unbound

At https://github.com/JelleZijlstra/taxonomy/blob/9b359fac68b982f5dddd60d1b10e4089607dd571/taxonomy/shell.py#L2169 . But the function assigns to o in both the try and except blocks; it's always defined.

Start with taxonomy/shell.py at line 2169 and reproduce the names_unbound diagnostic for function occ. Trace Basilisk's handling of assignments across the try and except blocks, then verify that this case no longer reports an unbound variable while genuine conditional-path cases still do.