In Python 2.6, a list comprehension was implemented in the current scope using a temporary _[1] variable to hold the list object:

>>> import dis
>>> dis.dis(compile('[x for x in y]', '?', 'exec'))
  1           0 BUILD_LIST               0
              3 DUP_TOP
              4 STORE_NAME               0 (_[1])
              7 LOAD_NAME                1 (y)
             10 GET_ITER
        >>   11 FOR_ITER                13 (to 27)
             14 STORE_NAME               2 (x)
             17 LOAD_NAME                0 (_[1])
             20 LOAD_NAME                2 (x)
             23 LIST_APPEND
             24 JUMP_ABSOLUTE           11
        >>   27 DELETE_NAME              0 (_[1])
             30 POP_TOP
             31 LOAD_CONST               0 (None)
             34 RETURN_VALUE

Nick Cochlan moved comprehensions into a separate scope in #1660500, and removed the need for a temporary variable in the process (the list / dict / set lives only on the stack).

However, the symbol table generates the _[1] name:

>>> import symtable
>>> symtable.symtable('[x for x in y]', '?', 'exec').get_children()[0].get_symbols()
[<symbol '.0'>, <symbol '_[1]'>, <symbol 'x'>]

Can this be dropped? I think all temporary variable handling can be ripped out.

We still need to the ".0" style temporary variables that are used for argument names in the implicitly generated functions, but it's definitely plausible that we're not actually using the "_[1]" style hidden variables anywhere anymore.

New changeset 3a087beddd9f0955eb9080a6fd1499ff89ca74bf by Nick Coghlan (Nitish Chandra) in branch 'master':
bpo-32836: Remove obsolete code from symtable pass (GH-5680)
https://github.com/python/cpython/commit/3a087beddd9f0955eb9080a6fd1499ff89ca74bf

New changeset 5506d603021518eaaa89e7037905f7a698c5e95c by Miss Islington (bot) in branch '3.7':
bpo-32836: Remove obsolete code from symtable pass (GH-5680)
https://github.com/python/cpython/commit/5506d603021518eaaa89e7037905f7a698c5e95c