Bug report
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CPython versions tested on:
3.12
Operating systems tested on:
Linux
Output from running 'python -VV' on the command line:
Python 3.12.0rc1 (main, Aug 16 2023, 05:03:59) [GCC 12.2.0]
A clear and concise description of the bug:
I have code that writes out sections of a data file in chunks, and uses seeks to ensure that the position is correct before writing.
In the following example, I write 5 bytes, seek to position 5 and write five more bytes. If I flush the buffer, the result is as expected. If I do not, 5 null bytes are written between the two groups of intended bytes.
#!/usr/bin/env python
import io
import gzip
for flush in (True, False):
data = io.BytesIO()
gzip_writer = gzip.GzipFile(fileobj=data, mode='wb')
gzip_writer.write(b'abcde')
# If the buffer isn't flushed, seek works from unchanged offset
if flush and hasattr(gzip_writer, '_buffer'):
gzip_writer._buffer.flush()
gzip_writer.seek(5)
gzip_writer.write(b'fghij')
gzip_writer.close()
# Recover result
data.seek(0)
gzip_reader = gzip.GzipFile(fileobj=data, mode='rb')
result = gzip_reader.read()
print(f'{flush=}: {result}')In the case where I seek but don't tell, I get spurious \x00 bytes:
flush=True: b'abcdefghij'
flush=False: b'abcde\x00\x00\x00\x00\x00fghij'
Here is the output in Python 3.10.10:
flush=True: b'abcdefghij'
flush=False: b'abcdefghij'
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Bug report
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and am confident this bug has not been reported before
CPython versions tested on:
3.12
Operating systems tested on:
Linux
Output from running 'python -VV' on the command line:
Python 3.12.0rc1 (main, Aug 16 2023, 05:03:59) [GCC 12.2.0]
A clear and concise description of the bug:
I have code that writes out sections of a data file in chunks, and uses seeks to ensure that the position is correct before writing.
In the following example, I write 5 bytes, seek to position 5 and write five more bytes. If I flush the buffer, the result is as expected. If I do not, 5 null bytes are written between the two groups of intended bytes.
In the case where I seek but don't tell, I get spurious
\x00bytes:Here is the output in Python 3.10.10:
Linked PRs