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PERF: Cache MultiIndex.levels #31651

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Feb 4, 2020
Merged

PERF: Cache MultiIndex.levels #31651

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PERF: Cache MultiIndex.levels
TomAugspurger Feb 4, 2020
cbc3d45
fixup tests
TomAugspurger Feb 4, 2020
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8 changes: 7 additions & 1 deletion pandas/core/indexes/multi.py
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Original file line number Diff line number Diff line change
Expand Up @@ -677,8 +677,11 @@ def __len__(self) -> int:
# --------------------------------------------------------------------
# Levels Methods

@property
@cache_readonly
def levels(self):
# Use cache_readonly to ensure that self.get_locs doesn't repeatedly
# create new IndexEngine
# https://github.com/pandas-dev/pandas/issues/31648
result = [
x._shallow_copy(name=name) for x, name in zip(self._levels, self._names)
]
Expand Down Expand Up @@ -1302,6 +1305,9 @@ def _set_names(self, names, level=None, validate=True):
)
self._names[lev] = name

# If .levels has been accessed, the names in our cache will be stale.
self._reset_cache()

names = property(
fset=_set_names, fget=_get_names, doc="""\nNames of levels in MultiIndex.\n"""
)
Expand Down
2 changes: 1 addition & 1 deletion pandas/tests/indexes/multi/test_get_set.py
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Expand Up @@ -159,7 +159,7 @@ def test_set_levels_codes_directly(idx):
minor_codes = [(x + 1) % 1 for x in minor_codes]
new_codes = [major_codes, minor_codes]

msg = "can't set attribute"
msg = "[Cc]an't set attribute"
with pytest.raises(AttributeError, match=msg):
idx.levels = new_levels
with pytest.raises(AttributeError, match=msg):
Expand Down