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Reset file pointer to 0 when reading file stream #7304

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merged 8 commits into from
Dec 1, 2022
+10 −21
Merged

Reset file pointer to 0 when reading file stream #7304

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4283b95
Reset file pointer to 0 when reading file stream
weiji14 Nov 21, 2022
68989c3
Expect warning rather than ValueError for test_open_twice
weiji14 Nov 21, 2022
befda31
Remove checks for errors raised in test_open_fileobj
weiji14 Nov 21, 2022
6f6fbe6
Fix typo form -> from
weiji14 Nov 21, 2022
93711b7
Add changelog entry for bugfix
weiji14 Nov 21, 2022
d2e84d2
Merge branch 'main' into fix_s3_start_byte
weiji14 Nov 29, 2022
929cb62
Remove warning about resetting file pointer to zero
weiji14 Nov 29, 2022
4e6e59c
Merge branch 'main' into fix_s3_start_byte
weiji14 Nov 29, 2022
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4 changes: 3 additions & 1 deletion xarray/core/utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -654,9 +654,11 @@ def read_magic_number_from_file(filename_or_obj, count=8) -> bytes:
magic_number = filename_or_obj[:count]
elif isinstance(filename_or_obj, io.IOBase):
if filename_or_obj.tell() != 0:
raise ValueError(
filename_or_obj.seek(0)
warnings.warn(
"cannot guess the engine, "
"file-like object read/write pointer not at the start of the file, "
"so resetting file pointer to zero. If this does not work, "
"please close and reopen, or use a context manager"
)
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@weiji14 weiji14 Nov 21, 2022 •
edited
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Is a warning actually necessary here, or can we remove the warning and let the file pointer reset to zero silently?

Edit: warning has been removed in 929cb62

magic_number = filename_or_obj.read(count)
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12 changes: 2 additions & 10 deletions xarray/tests/test_backends.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3031,7 +3031,7 @@ def test_open_badbytes(self) -> None:
def test_open_twice(self) -> None:
expected = create_test_data()
expected.attrs["foo"] = "bar"
with pytest.raises(ValueError, match=r"read/write pointer not at the start"):
with pytest.warns(match=r"read/write pointer not at the start"):
with create_tmp_file() as tmp_file:
expected.to_netcdf(tmp_file, engine="h5netcdf")
with open(tmp_file, "rb") as f:
Expand Down Expand Up @@ -3069,15 +3069,7 @@ def test_open_fileobj(self) -> None:
# `raises_regex`?). Ref https://github.com/pydata/xarray/pull/5191
with open(tmp_file, "rb") as f:
f.seek(8)
with pytest.raises(
ValueError,
match="match in any of xarray's currently installed IO",
):
with pytest.warns(
RuntimeWarning,
match=re.escape("'h5netcdf' fails while guessing"),
):
open_dataset(f)
open_dataset(f)


@requires_h5netcdf
Expand Down