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TST: Raise ValueError and suggestion to use header=None if header=-1 is pa… #27878

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Merged
merged 5 commits into from
Aug 15, 2019
Merged

TST: Raise ValueError and suggestion to use header=None if header=-1 is pa… #27878

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878f550
Make comment about previous version more specific
Aug 14, 2019
a642363
Document change in whatsnew file
Aug 14, 2019
9f58612
Update doc/source/whatsnew/v0.25.1.rst
MarcoGorelli Aug 14, 2019
dfecd26
Add issue number to test as comment
MarcoGorelli Aug 14, 2019
fee3444
Revise fix so it checks that header is non-negative integer (or list-…
MarcoGorelli Aug 15, 2019
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v0.25.1.rst
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Expand Up @@ -105,7 +105,7 @@ I/O
^^^

- Avoid calling ``S3File.s3`` when reading parquet, as this was removed in s3fs version 0.3.0 (:issue:`27756`)
-
- Better error message when a negative header is passed in :func:`pandas.read_csv` (:issue:`27779`)
-

Plotting
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6 changes: 6 additions & 0 deletions pandas/io/common.py
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Expand Up @@ -125,6 +125,12 @@ def _validate_header_arg(header) -> None:
"the row(s) making up the column names"
)

# In version 0.24, this would have worked.
if header == -1:
raise ValueError(
"Passing -1 to header is invalid. For no header, use header=None instead"
)


def _stringify_path(
filepath_or_buffer: FilePathOrBuffer[AnyStr]
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15 changes: 15 additions & 0 deletions pandas/tests/io/parser/test_header.py
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Expand Up @@ -24,6 +24,21 @@ def test_read_with_bad_header(all_parsers):
parser.read_csv(s, header=[10])


def test_negative_header(all_parsers):
# see gh-27779
parser = all_parsers
data = """1,2,3,4,5
6,7,8,9,10
11,12,13,14,15
"""
with pytest.raises(
ValueError,
match="Passing -1 to header is invalid. "
"For no header, use header=None instead",
):
parser.read_csv(StringIO(data), header=-1)


@pytest.mark.parametrize("header", [True, False])
def test_bool_header_arg(all_parsers, header):
# see gh-6114
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