Copilot commented on code in PR #50430:
URL: https://github.com/apache/arrow/pull/50430#discussion_r3547640283
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python/pyarrow/array.pxi:
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@@ -3551,6 +3613,52 @@ cdef class MapArray(ListArray):
Concrete class for Arrow arrays of a map data type.
"""
+ cdef object _getitem_py(self, int64_t i, object maps_as_pydicts):
+ cdef CListArray* arr = <CListArray*> self.ap
+ cdef bint as_dicts = maps_as_pydicts is not None
+ if as_dicts and maps_as_pydicts != "lossy" and maps_as_pydicts !=
"strict":
+ # Matches MapScalar.as_py, which validates before the null check.
+ raise ValueError(
+ "Invalid value for 'maps_as_pydicts': "
+ + "valid values are 'lossy', 'strict' or `None` (default). "
+ + f"Received {maps_as_pydicts!r}."
+ )
+ if arr.IsNull(i):
+ return None
+ if self._children_cache is None:
+ self._children_cache = (self.keys, self.items)
+ cdef Array keys = <Array> (<tuple> self._children_cache)[0]
+ cdef Array items = <Array> (<tuple> self._children_cache)[1]
+ cdef int64_t j, start = arr.value_offset(i), end = arr.value_offset(i
+ 1)
+ if not as_dicts:
+ # Matches MapScalar.as_py with the default maps_as_pydicts=None:
+ # an association list of (key, value) tuples.
+ return [
+ (keys._getitem_py(j, None), items._getitem_py(j,
maps_as_pydicts))
+ for j in range(start, end)
+ ]
+ cdef dict result = {}
+ for j in range(start, end):
+ result[keys._getitem_py(j, None)] = items._getitem_py(j,
maps_as_pydicts)
+ if len(result) == end - start:
+ return result
+ # Duplicate keys: redo the row with the per-key loop so the 'lossy'
+ # warnings and 'strict' KeyError match MapScalar.as_py exactly.
+ result = {}
+ for j in range(start, end):
+ key = keys._getitem_py(j, None)
+ if key in result:
+ if maps_as_pydicts == "strict":
+ raise KeyError(
+ "Converting to Python dictionary is not supported in
strict mode "
+ f"when duplicate keys are present (duplicate key was
'{key}')."
+ )
+ else:
+ warnings.warn(
+ f"Encountered key '{key}' which was already
encountered.")
+ result[key] = items._getitem_py(j, maps_as_pydicts)
+ return result
Review Comment:
In the dict conversion fast path, values are converted before duplicate keys
are detected. This changes MapScalar.as_py semantics for both 'strict' and
'lossy': MapScalar checks for duplicates (and raises/warns) *before* converting
the duplicate entry’s value, but the current first pass may raise from value
conversion (or skip the warning) before the duplicate-key handling runs.
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