On 08.04.2021 23:31, Ethan Furman wrote:
In issue14243 [1] there are two issues being tracked:
- the difference in opening shared files between posix and Windows
- the behavior of closing the underlying file in the middle of
NamedTemporaryFile's context management
I'd like to address and get feedback on the context management issue.
```python
from tempfile import NamedTemporaryFile
with NamedTemporaryFile() as fp:
fp.write(b'some data')
fp = open(fp.name())
data = fp.read()
assert data == 'some_data'
```
Occasionally, it is desirable to close and reopen the temporary file in order to read the contents (there are OSes that cannot open a temp
file for reading while it is still open for writing). This would look like:
What's the problem with `NamedTemporaryFile(mode='w+b')`? (it's actually the
default!)
You can both read and write without reopening.
If you don't want to seek() between reading and writing, you can dup() the descriptor and wrap it with another file object:
`fp2=open(os.dup(fp.file.fileno()))`
```python
from tempfile import NamedTemporaryFile
with NamedTemporaryFile() as fp:
fp.write(b'some data')
fp.close() # Windows workaround
fp.open()
data = fp.read()
assert data == 'some_data'
```
The problem is that, even though `fp.open()` is still inside the context manager, the `close()` call deletes the file [2]. To handle this
scenario, my proposal is two-fold:
1) stop using the TEMPFILE OS attribute so the OS doesn't delete the file on
close
2) add `.open()` to NamedTemporaryFile
A possible side effect of (1) is that temp files may accumulate if the interpreter crashes, but given the file-management abilities in
today's software that seems like a minor annoyance at most.
The backwards compatibility issue of (1) is that the file is no longer deleted after a manual `close()` -- but why one would call close()
and then stay inside the CM, outside of testing, I cannot fathom. [3]
So, opinions on modifying NamedTemporaryFile to not delete on close() if inside
a CM, and add open() ?
--
~Ethan~
[1] https://bugs.python.org/issue14243
[2] plus, the `.open()` doesn't yet exist
[3] feel free to educate me :-)
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--
Regards,
Ivan
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