open_fs(".", writeable=False) returns an FS object which can write

[mezhaka]

I'd like to have read-only FS, however I am able to do

from fs.opener import open_fs
with open_fs(".", writeable=False) as fs_:
    fs_.writetext("spam", "vikings")

I'd expect it to fail, like the

from fs.wrap import read_only, WrapReadOnly
r = read_only(fs_)
r.writetext("spam", "vikings")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/mnt/disks/repo/bin/miniconda3/envs/deeplearning/lib/python3.8/site-packages/fs/wrap.py", line 221, in writetext
    raise ResourceReadOnly(path)
fs.errors.ResourceReadOnly: resource 'spam' is read only

[lurch]

I've had a quick search through the code-base, and it looks like most "openers" simply ignore the writeable parameter, and it seems to be only e.g. tarfs and zipfs where the same "FS" can't be both read-and-write-at-the-same-time that actually use the writeable parameter.

As you've seen, you can achieve what you want with the read_only WrapFS, so maybe this is just a documentation issue?

[willmcgugan]

This is what the docs say...

writeable (bool, optional) – True if the filesystem must be writeable.

So if writable=True the filesystem will be writable, but the inverse isn't necessarily true. i.e. writable=False means it doesn't need to be writable (but it could be). A documentation issue perhaps. Open to adding something to clarify.

[althonos]

I updated the documentation for fs.open_fs with a section specifically about this. It now says:

Caution:
        The ``writeable`` parameter only controls whether the
        filesystem *needs* to be writable, which is relevant for
        some archive filesystems. Passing ``writeable=False`` will
        **not** make the return filesystem read-only. For this,
        consider using `fs.wrap.read_only` to wrap the returned
        instance.