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bpo-39320: Fix changes in the evaluation logic of unpacking operations. #18264

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bpo-39320: Fix changes in the evaluation logic of unpacking operations. #18264

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af88a4e
Add failing regression tests.
brandtbucher Jan 29, 2020
f53d264
Visit all nodes *before* merging.
brandtbucher Jan 30, 2020
d515ca9
Regenerate importlib.
brandtbucher Jan 30, 2020
1fcb02a
Simplify test.
brandtbucher Jan 30, 2020
34f9208
Add NEWS entry.
brandtbucher Jan 30, 2020
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39 changes: 39 additions & 0 deletions Lib/test/test_unpack_ex.py
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Expand Up @@ -335,6 +335,45 @@
...
SyntaxError: can't use starred expression here

Check for correct execution order (all fail):

>>> x = None
>>> try:
... [*x, *print("This should be printed!")]
... except TypeError:
... pass
This should be printed!

>>> try:
... (*x, *print("This should be printed!"))
... except TypeError:
... pass
This should be printed!

>>> try:
... {*x, *print("This should be printed!")}
... except TypeError:
... pass
This should be printed!

>>> try:
... f(*x, *print("This should be printed!"))
... except TypeError:
... pass
This should be printed!

>>> try:
... {**x, **print("This should be printed!")}
... except TypeError:
... pass
This should be printed!

>>> try:
... f(**x, **print("This should be printed!"))
... except TypeError:
... pass
This should be printed!

Some size constraints (all fail.)

>>> s = ", ".join("a%d" % i for i in range(1<<8)) + ", *rest = range(1<<8 + 1)"
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-01-29-16-48-41.bpo-39320.Pm4UhU.rst
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@@ -0,0 +1 @@
Fix a regression in the evaluation order of :pep:`448` unpacking syntax.
98 changes: 45 additions & 53 deletions Python/compile.c
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Expand Up @@ -3710,43 +3710,34 @@ starunpack_helper(struct compiler *c, asdl_seq *elts, int pushed,
for (i = 0; i < n; i++) {
expr_ty elt = asdl_seq_GET(elts, i);
if (elt->kind == Starred_kind) {
ADDOP_I(c, build, pushed);
seen_star = 1;
break;
}
}
for (i = 0; i < n; i++) {
expr_ty elt = asdl_seq_GET(elts, i);
if (elt->kind == Starred_kind) {
VISIT(c, expr, elt->v.Starred.value);
}
else {
VISIT(c, expr, elt);
}
}
if (seen_star) {
seen_star = 0;
/* Reverse the stack: */
ADDOP_I(c, BUILD_TUPLE, n);
ADDOP_I(c, UNPACK_SEQUENCE, n);
for (i = 0; i < n; i++) {
expr_ty elt = asdl_seq_GET(elts, i);
if (elt->kind == Starred_kind) {
if (seen_star == 0) {
ADDOP_I(c, build, i+pushed);
seen_star = 1;
}
VISIT(c, expr, elt->v.Starred.value);
ADDOP_I(c, extend, 1);
}
else {
VISIT(c, expr, elt);
if (seen_star) {
ADDOP_I(c, add, 1);
}
}
ADDOP_I(c, elt->kind == Starred_kind ? extend : add, n-i);
}
assert(seen_star);
if (tuple) {
ADDOP(c, LIST_TO_TUPLE);
}
}
else {
for (i = 0; i < n; i++) {
expr_ty elt = asdl_seq_GET(elts, i);
VISIT(c, expr, elt);
}
if (tuple) {
ADDOP_I(c, BUILD_TUPLE, n+pushed);
} else {
ADDOP_I(c, build, n+pushed);
}
ADDOP_I(c, tuple ? BUILD_TUPLE : build, n+pushed);
}
return 1;
}
Expand Down Expand Up @@ -3867,40 +3858,33 @@ static int
compiler_dict(struct compiler *c, expr_ty e)
{
Py_ssize_t i, n, elements;
int have_dict;
int is_unpacking = 0;
n = asdl_seq_LEN(e->v.Dict.values);
have_dict = 0;
elements = 0;
int to_merge = 0;
for (i = 0; i < n; i++) {
is_unpacking = (expr_ty)asdl_seq_GET(e->v.Dict.keys, i) == NULL;
if (is_unpacking) {
if (elements) {
if (!compiler_subdict(c, e, i - elements, i)) {
return 0;
}
if (have_dict) {
ADDOP_I(c, DICT_UPDATE, 1);
}
have_dict = 1;
to_merge++;
elements = 0;
}
if (have_dict == 0) {
if (to_merge == 0) {
ADDOP_I(c, BUILD_MAP, 0);
have_dict = 1;
to_merge++;
}
VISIT(c, expr, (expr_ty)asdl_seq_GET(e->v.Dict.values, i));
ADDOP_I(c, DICT_UPDATE, 1);
to_merge++;
}
else {
if (elements == 0xFFFF) {
if (!compiler_subdict(c, e, i - elements, i)) {
return 0;
}
if (have_dict) {
ADDOP_I(c, DICT_UPDATE, 1);
}
have_dict = 1;
to_merge++;
elements = 0;
}
else {
Expand All @@ -3912,13 +3896,17 @@ compiler_dict(struct compiler *c, expr_ty e)
if (!compiler_subdict(c, e, n - elements, n)) {
return 0;
}
if (have_dict) {
ADDOP_I(c, DICT_UPDATE, 1);
}
have_dict = 1;
to_merge++;
}
if (!have_dict) {
if (!to_merge) {
ADDOP_I(c, BUILD_MAP, 0);
} else if (--to_merge) {
/* Reverse the stack. */
ADDOP_I(c, BUILD_TUPLE, to_merge)
ADDOP_I(c, UNPACK_SEQUENCE, to_merge)
while (to_merge) {
ADDOP_I(c, DICT_UPDATE, to_merge--);
}
}
return 1;
}
Expand Down Expand Up @@ -4283,8 +4271,7 @@ compiler_call_helper(struct compiler *c,
}
/* Then keyword arguments */
if (nkwelts) {
/* Has a new dict been pushed */
int have_dict = 0;
int to_merge = 0;

nseen = 0; /* the number of keyword arguments on the stack following */
for (i = 0; i < nkwelts; i++) {
Expand All @@ -4295,15 +4282,15 @@ compiler_call_helper(struct compiler *c,
if (!compiler_subkwargs(c, keywords, i - nseen, i)) {
return 0;
}
have_dict = 1;
to_merge++;
nseen = 0;
}
if (!have_dict) {
if (!to_merge) {
ADDOP_I(c, BUILD_MAP, 0);
have_dict = 1;
to_merge++;
}
VISIT(c, expr, kw->value);
ADDOP_I(c, DICT_MERGE, 1);
to_merge++;
}
else {
nseen++;
Expand All @@ -4314,12 +4301,17 @@ compiler_call_helper(struct compiler *c,
if (!compiler_subkwargs(c, keywords, nkwelts - nseen, nkwelts)) {
return 0;
}
if (have_dict) {
ADDOP_I(c, DICT_MERGE, 1);
to_merge++;
}
assert(to_merge);
if (--to_merge) {
/* Reverse the stack: */
ADDOP_I(c, BUILD_TUPLE, to_merge)
ADDOP_I(c, UNPACK_SEQUENCE, to_merge)
while (to_merge) {
ADDOP_I(c, DICT_MERGE, to_merge--);
}
have_dict = 1;
}
assert(have_dict);
}
ADDOP_I(c, CALL_FUNCTION_EX, nkwelts > 0);
return 1;
Expand Down