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fallback: pass object_pairs_hook a list of pairs #744

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Merged
methane merged 1 commit into from
Oct 2, 2026
Merged

fallback: pass object_pairs_hook a list of pairs #744

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fallback: pass object_pairs_hook a list of pairs 
The pure-Python Unpacker passed a generator, so a hook that read the
pairs twice saw nothing the second time, indexing raised TypeError, and
a hook that ignored its argument left the map body unread. The C
extension and the docstring give a list.
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@youdie006
youdie006 committed Oct 2, 2026
commit cf43f17ed5fed61a42f2c31fa7222258d9452b72
18 changes: 9 additions & 9 deletions msgpack/fallback.py
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Original file line number Diff line number Diff line change
Expand Up @@ -529,15 +529,15 @@ def _unpack(self, execute=EX_CONSTRUCT):
self._unpack(EX_SKIP)
return
if self._object_pairs_hook is not None:

def _gen():
for _ in range(n):
key = self._unpack(EX_CONSTRUCT)
if self._strict_map_key and type(key) not in (str, bytes):
raise ValueError("%s is not allowed for map key" % str(type(key)))
yield key, self._unpack(EX_CONSTRUCT)

ret = self._object_pairs_hook(_gen())
# Pass a list, as the C extension does, so the whole map is
# consumed even if the hook does not iterate it.
pairs = []
for _ in range(n):
key = self._unpack(EX_CONSTRUCT)
if self._strict_map_key and type(key) not in (str, bytes):
raise ValueError("%s is not allowed for map key" % str(type(key)))
pairs.append((key, self._unpack(EX_CONSTRUCT)))
ret = self._object_pairs_hook(pairs)
else:
ret = {}
for _ in range(n):
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12 changes: 12 additions & 0 deletions test/test_obj.py
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,18 @@ def test_decode_pairs_hook():
assert unpacked[1] == prod_sum


def test_decode_pairs_hook_receives_list():
def reject_duplicate_keys(pairs):
keys = [k for k, _ in pairs]
assert len(keys) == len(set(keys))
return dict(pairs)

packed = packb([{"a": 1, "b": 2}, 3])
assert unpackb(packed, object_pairs_hook=reject_duplicate_keys) == [{"a": 1, "b": 2}, 3]
assert unpackb(packed, object_pairs_hook=lambda pairs: pairs[0]) == [("a", 1), 3]
assert unpackb(packed, object_pairs_hook=lambda pairs: None) == [None, 3]


def test_only_one_obj_hook():
with raises(TypeError):
unpackb(b"", object_hook=lambda x: x, object_pairs_hook=lambda x: x)
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