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[3.9] bpo-40715: Reject dict unpacking on dict comprehensions (GH-20292) #20303

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Merged
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May 21, 2020
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[3.9] bpo-40715: Reject dict unpacking on dict comprehensions (GH-20292) #20303

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15 changes: 10 additions & 5 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -499,14 +499,16 @@ setcomp[expr_ty]:
| '{' a=expression b=for_if_clauses '}' { _Py_SetComp(a, b, EXTRA) }
| invalid_comprehension
dict[expr_ty]:
| '{' a=[kvpairs] '}' { _Py_Dict(CHECK(_PyPegen_get_keys(p, a)),
CHECK(_PyPegen_get_values(p, a)), EXTRA) }
| '{' a=[double_starred_kvpairs] '}' {
_Py_Dict(CHECK(_PyPegen_get_keys(p, a)), CHECK(_PyPegen_get_values(p, a)), EXTRA) }
dictcomp[expr_ty]:
| '{' a=kvpair b=for_if_clauses '}' { _Py_DictComp(a->key, a->value, b, EXTRA) }
kvpairs[asdl_seq*]: a=','.kvpair+ [','] { a }
kvpair[KeyValuePair*]:
| invalid_dict_comprehension
double_starred_kvpairs[asdl_seq*]: a=','.double_starred_kvpair+ [','] { a }
double_starred_kvpair[KeyValuePair*]:
| '**' a=bitwise_or { _PyPegen_key_value_pair(p, NULL, a) }
| a=expression ':' b=expression { _PyPegen_key_value_pair(p, a, b) }
| kvpair
kvpair[KeyValuePair*]: a=expression ':' b=expression { _PyPegen_key_value_pair(p, a, b) }
for_if_clauses[asdl_seq*]:
| for_if_clause+
for_if_clause[comprehension_ty]:
Expand Down Expand Up @@ -657,6 +659,9 @@ invalid_block:
invalid_comprehension:
| ('[' | '(' | '{') a=starred_expression for_if_clauses {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "iterable unpacking cannot be used in comprehension") }
invalid_dict_comprehension:
| '{' a='**' bitwise_or for_if_clauses '}' {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "dict unpacking cannot be used in dict comprehension") }
invalid_parameters:
| param_no_default* (slash_with_default | param_with_default+) param_no_default {
RAISE_SYNTAX_ERROR("non-default argument follows default argument") }
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5 changes: 5 additions & 0 deletions Lib/test/test_unpack_ex.py
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Original file line number Diff line number Diff line change
Expand Up @@ -158,6 +158,11 @@
...
SyntaxError: iterable unpacking cannot be used in comprehension

>>> {**{} for a in [1]}
Traceback (most recent call last):
...
SyntaxError: dict unpacking cannot be used in dict comprehension

# Pegen is better here.
# Generator expression in function arguments

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