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[3.8] bpo-38640: Allow break and continue in always false while loops (GH-16992) #16993

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Merged
miss-islington merged 1 commit into from
Oct 30, 2019
Merged

[3.8] bpo-38640: Allow break and continue in always false while loops (GH-16992) #16993

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18 changes: 18 additions & 0 deletions Lib/test/test_compile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -731,6 +731,24 @@ def unused_block_while_else():
self.assertEqual(None, opcodes[0].argval)
self.assertEqual('RETURN_VALUE', opcodes[1].opname)

def test_false_while_loop(self):
def break_in_while():
while False:
break

def continue_in_while():
while False:
continue

funcs = [break_in_while, continue_in_while]

# Check that we did not raise but we also don't generate bytecode
for func in funcs:
opcodes = list(dis.get_instructions(func))
self.assertEqual(2, len(opcodes))
self.assertEqual('LOAD_CONST', opcodes[0].opname)
self.assertEqual(None, opcodes[0].argval)
self.assertEqual('RETURN_VALUE', opcodes[1].opname)

class TestExpressionStackSize(unittest.TestCase):
# These tests check that the computed stack size for a code object
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-10-30-11-25-25.bpo-38640.4sAFh5.rst
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@@ -0,0 +1,3 @@
Fixed a bug in the compiler that was causing to raise in the presence of
break statements and continue statements inside always false while loops.
Patch by Pablo Galindo.
8 changes: 8 additions & 0 deletions Python/compile.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2736,7 +2736,15 @@ compiler_while(struct compiler *c, stmt_ty s)

if (constant == 0) {
BEGIN_DO_NOT_EMIT_BYTECODE
// Push a dummy block so the VISIT_SEQ knows that we are
// inside a while loop so it can correctly evaluate syntax
// errors.
if (!compiler_push_fblock(c, WHILE_LOOP, NULL, NULL)) {
return 0;
}
VISIT_SEQ(c, stmt, s->v.While.body);
// Remove the dummy block now that is not needed.
compiler_pop_fblock(c, WHILE_LOOP, NULL);
END_DO_NOT_EMIT_BYTECODE
if (s->v.While.orelse) {
VISIT_SEQ(c, stmt, s->v.While.orelse);
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