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CLN: Ensure that setitem ops don't coerce values #51671

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Merged
merged 2 commits into from
Feb 28, 2023
Merged

CLN: Ensure that setitem ops don't coerce values #51671

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CLN: Ensure that setitem ops don't coerce values
phofl Feb 27, 2023
3365a61
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phofl Feb 27, 2023
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16 changes: 11 additions & 5 deletions pandas/core/frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4757,6 +4757,14 @@ def insert(
if not isinstance(loc, int):
raise TypeError("loc must be int")

if isinstance(value, DataFrame) and len(value.columns) > 1:
raise ValueError(
f"Expected a one-dimensional object, got a DataFrame with "
f"{len(value.columns)} instead."
)
elif isinstance(value, DataFrame):
value = value.iloc[:, 0]

value = self._sanitize_column(value)
self._mgr.insert(loc, column, value)

Expand Down Expand Up @@ -4843,11 +4851,9 @@ def _sanitize_column(self, value) -> ArrayLike:
"""
self._ensure_valid_index(value)

# We can get there through isetitem with a DataFrame
# or through loc single_block_path
if isinstance(value, DataFrame):
return _reindex_for_setitem(value, self.index)
elif is_dict_like(value):
# Using a DataFrame would mean coercing values to one dtype
assert not isinstance(value, DataFrame)
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no other cases that can be affected by disallowing this here?

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None that I can think of or find. Isetitem iterates over the columns now. Don’t think that we can get here with a DataFrame now

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Thanks for checking.

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Not for this PR, but some things I saw while double-checking:

in isetitem isinstance(value, DataFrame) case should we check that len(loc) == len(value.columns)?
_iset_item is only called from _replace_columnwise, where we know we have a Series with matching index, might be simpler to skip sanitize_column?
Might make sense to refactor _set_item back into __setitem__, as the latter isn't that complicated and the former has a name really similar to a bunch of other names

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  1. Yes we should probably raise if they don't match
  2. Should be faster at least
  3. Makes setitem pretty long, but shouldn't really hurt?

if is_dict_like(value):
return _reindex_for_setitem(Series(value), self.index)

if is_list_like(value):
Expand Down
2 changes: 1 addition & 1 deletion pandas/tests/frame/indexing/test_insert.py
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Expand Up @@ -100,6 +100,6 @@ def test_insert_frame(self):
# GH#42403
df = DataFrame({"col1": [1, 2], "col2": [3, 4]})

msg = r"Expected a 1D array, got an array with shape \(2, 2\)"
msg = "Expected a one-dimensional object, got a DataFrame with 2 instead."
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"2" here sounds like it is referring to 2 dimensions, which is accurate but i think not intended

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Yikes yes, I forgot to add columns, thx

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Updated, otherwise ok?

I think making this stricter helps in the long run

with pytest.raises(ValueError, match=msg):
df.insert(1, "newcol", df)