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REGR: Avoid error when defining non existing usecols with python engine #41244

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Merged
merged 1 commit into from
May 12, 2021
Merged

REGR: Avoid error when defining non existing usecols with python engine #41244

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15 changes: 10 additions & 5 deletions pandas/io/parsers/python_parser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -299,10 +299,10 @@ def _exclude_implicit_index(self, alldata):
# error: Cannot determine type of 'index_col'
offset = len(self.index_col) # type: ignore[has-type]

if self._col_indices is not None and len(names) != len(self._col_indices):
names = [names[i] for i in sorted(self._col_indices)]

return {name: alldata[i + offset] for i, name in enumerate(names)}, names
len_alldata = len(alldata)
return {
name: alldata[i + offset] for i, name in enumerate(names) if i < len_alldata
}, names

# legacy
def get_chunk(self, size=None):
Expand Down Expand Up @@ -473,7 +473,12 @@ def _infer_columns(self):
self._handle_usecols(columns, names)
else:
num_original_columns = len(names)
columns = [names]
if self._col_indices is not None and len(names) != len(
self._col_indices
):
columns = [[names[i] for i in sorted(self._col_indices)]]
else:
columns = [names]
else:
columns = self._handle_usecols(columns, columns[0])
else:
Expand Down
15 changes: 15 additions & 0 deletions pandas/tests/io/parser/usecols/test_usecols_basic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -373,3 +373,18 @@ def test_usecols_subset_names_mismatch_orig_columns(all_parsers, usecols):
result = parser.read_csv(StringIO(data), header=0, names=names, usecols=usecols)
expected = DataFrame({"A": [1, 5], "C": [3, 7]})
tm.assert_frame_equal(result, expected)


@pytest.mark.parametrize("names", [None, ["a", "b"]])
def test_usecols_indices_out_of_bounds(all_parsers, names):
# GH#25623
parser = all_parsers
data = """
a,b
1,2
"""
result = parser.read_csv(StringIO(data), usecols=[0, 2], names=names, header=0)
expected = DataFrame({"a": [1], "b": [None]})
if names is None and parser.engine == "python":
expected = DataFrame({"a": [1]})
tm.assert_frame_equal(result, expected)