[issue43069] Python fails to read a script whose path is `/dev/fd/X`
Alexey Izbyshev added the comment:
I would suggest to start digging from the following piece of code in
`maybe_pyc_file()` (Python/pythonrun.c):
int ispyc = 0;
if (ftell(fp) == 0) {
if (fread(buf, 1, 2, fp) == 2 &&
((unsigned int)buf[1]<<8 | buf[0]) == halfmagic)
ispyc = 1;
rewind(fp);
}
--
nosy: +izbyshev
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[issue43069] Python fails to read a script whose path is `/dev/fd/X`
Ronald Oussoren added the comment:
I can reproduce the issue on macOS 11.1.
As you write:
- running /dev/fd/X as a script fails silently if it refers to an smallish file
- reading /dev/fd/X referring to the same smallish files works fine (the
``open('/dev/fd/9').read()`` scenario.
If I read the code in Modules/main.c correctly the main difference between the
two scenario's is that the first scenario using the C stdio library to read the
file (in pymain_run_file_obj), and the latter uses the normal Python io stack.
Reading /dev/fd/9 works fine when using either stdio or open/read in C code.
I have not yet tried to untangle the layers of C code from pymain_run_file_obj
to actually reading the script, there might be something there that sheds light
on what's going on here.
I'm not yet willing to claim this is an OS bug as I've failed to reproduce this
outside of Python.
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[issue43069] Python fails to read a script whose path is `/dev/fd/X`
New submission from Ciprian Dorin Craciun :
Sometimes (especially from wrapper scripts) one would like to call Python with
a script that should be read from a file-descriptor, like `python3 /dev/fd/9`;
most likely the backing is a file in `TMPDIR` (perhaps unlinked, like `bash`'s
"here documents").
However on OSX (I've tried it on `10.15.7` and `10.13.6`), for some reason if
that script is too "large" (more than a couple of characters) it just bails
out, even if that file-descriptor is in fact backed by a file.
For example:
echo 'print("1234567890")' >/tmp/x.py && python3 /dev/fd/9 9/tmp/x.py && python3 /dev/fd/9 9
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