testing an open file

[Skaperen]

what kind of test can i apply (or what library should i look at) to be able to detect if a given open file is open for reading? it is passed as an argument to a function so the function does get to directly see how the file was opened.

[Larz60+]

you can get the mode (and much more) by using stats

for example (run from script path -- modify path as required --, probably better to use pathlib):
modified from example here: https://docs.python.org/3/library/os.html#os.scandir

import os

path = os.getcwd()
with os.scandir(path) as it:
    for entry in it:
        if not entry.name.startswith('.') and entry.is_file():
            stats = os.stat(path, follow_symlinks=False)
            print(stats)

see https://docs.python.org/3/library/stat.html on how to interpret the stat results.

[Gribouillis]

If the file was opened with the builtin function open(), it may have a mode attribute

>>> f = open('temp.tex')
>>> f.mode
'r'

[Skaperen]

i was wanting how it was opened, not what permissions the file allows me to open. it might be open to a non-file object like:

Output:
lt1a/forums/3 /home/forums 4> python3.8
Python 3.8.10 (default, Nov 14 2022, 12:59:47) 
[GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.stdin.mode,sys.stderr.mode,sys.stdout.mode
('r', 'w', 'w')
>>> 
lt1a/forums/3 /home/forums 5> 

what cases where it may not have a mode attribute?

[Gribouillis]

what cases where it may not have a mode attribute?

When the (pseudo) file object was not opened by the function open(), for example

>>> import io
>>> f = io.StringIO()
>>> f.mode
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: '_io.StringIO' object has no attribute 'mode'

[Skaperen]

it's an open file object. i want to see if i can read it without trying to read it. i think i might need the same for write.

[Gribouillis]

Objets subclassing io.IOBase have a .readable() method. This also applies to StringIO.

Pseudo file objects provided by third party code may have no readable() or writable() method.

[Skaperen]

so, i can just test for mode or a method and if neither exist, just raise an exception saying that readability cannot be determined. that should be workable for most common cases, i think. or am i guessing too far?