[New-bugs-announce] [issue23099] BytesIO and StringIO values unavailable when closed

[Martin Panter]

New submission from Martin Panter:

IOBase.close() doc says file operations raise ValueError, but it is not obvious to me that reading back the “file” buffer is a file operation.

>>> with BytesIO() as b:
...     b.write(b"123")
... 
3
>>> b.getvalue()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: I/O operation on closed file.

Even worse, the memoryview gets corrupted on close():

>>> b = BytesIO(b"123")
>>> m = b.getbuffer()
>>> b.close()
>>> bytes(m)
b'\x98\x02>'

I also noticed that in the “io” implementation, writing to the file seems to be completely disallowed, even if it would not seem to change the size:

>>> b = BytesIO(b"123")
>>> m = b.getbuffer()
>>> b.write(b"x")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
BufferError: Existing exports of data: object cannot be re-sized

----------
components: IO
messages: 233016
nosy: vadmium
priority: normal
severity: normal
status: open
title: BytesIO and StringIO values unavailable when closed
type: behavior
versions: Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue23099>
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