[3.7] Revert "closes bpo-27494: Fix 2to3 handling of trailing comma after a generator expression (GH-3771)" (GH-8241) by miss-islington · Pull Request #8580 · python/cpython

python

@@ -111,8 +111,8 @@ atom: ('(' [yield_expr|testlist_gexp] ')' | '{' [dictsetmaker] '}' | '`' testlist1 '`' | NAME | NUMBER | STRING+ | '.' '.' '.') listmaker: (test|star_expr) ( old_comp_for | (',' (test|star_expr))* [','] ) testlist_gexp: (test|star_expr) ( old_comp_for | (',' (test|star_expr))* [','] ) listmaker: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] ) testlist_gexp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] ) lambdef: 'lambda' [varargslist] ':' test trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME subscriptlist: subscript (',' subscript)* [','] @@ -142,28 +142,9 @@ argument: ( test [comp_for] | star_expr )
comp_iter: comp_for | comp_if comp_for: [ASYNC] 'for' exprlist 'in' or_test [comp_iter] comp_for: [ASYNC] 'for' exprlist 'in' testlist_safe [comp_iter] comp_if: 'if' old_test [comp_iter]
# As noted above, testlist_safe extends the syntax allowed in list # comprehensions and generators. We can't use it indiscriminately in all # derivations using a comp_for-like pattern because the testlist_safe derivation # contains comma which clashes with trailing comma in arglist. # # This was an issue because the parser would not follow the correct derivation # when parsing syntactically valid Python code. Since testlist_safe was created # specifically to handle list comprehensions and generator expressions enclosed # with parentheses, it's safe to only use it in those. That avoids the issue; we # can parse code like set(x for x in [],). # # The syntax supported by this set of rules is not a valid Python 3 syntax, # hence the prefix "old". # # See https://bugs.python.org/issue27494 old_comp_iter: old_comp_for | old_comp_if old_comp_for: [ASYNC] 'for' exprlist 'in' testlist_safe [old_comp_iter] old_comp_if: 'if' old_test [old_comp_iter]
testlist1: test (',' test)*
# not used in grammar, but may appear in "node" passed from Parser to Compiler