tox: bump the pinned flake8 and pylint version (SC-422)

[paride]

Proposed Commit Message

tox: bump the pinned flake8 and pylint version

* pylint: fix W1406 (redundant-u-string-prefix)

The u prefix for strings is no longer necessary in Python >=3.0.

* pylint: disable W1514 (unspecified-encoding)
    
From https://www.python.org/dev/peps/pep-0597/ (Python 3.10):
    
The new warning stems form https://www.python.org/dev/peps/pep-0597,
which says:
    
  Developers using macOS or Linux may forget that the default encoding
  is not always UTF-8. [...] Even Python experts may assume that the
  default encoding is UTF-8. This creates bugs that only happen on Windows.
    
The warning could be fixed by always specifying encoding='utf-8',
however we should be careful to not break environments which are not
utf-8 (or explicitly state that only utf-8 is supported). Let's silence
the warning for now.

* _quick_read_instance_id: cover the case where load_yaml() returns None

Spotted by pylint:
 - E1135 (unsupported-membership-test)
 - E1136 (unsubscriptable-object)

LP: #1944414

Additional Context

Spotted by the cloud-init-style-tip Jenkins job.

Test Steps

Reproduce with: tox -e tip-pylint. Test this branch by just running tox from it.

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[paride]

This is a WIP because I'm not sure on how to fix this:

************* Module cloudinit.sources.DataSourceNoCloud
cloudinit/sources/DataSourceNoCloud.py:250: [E1135(unsupported-membership-test), _quick_read_instance_id] Value 'md' doesn't support membership test
cloudinit/sources/DataSourceNoCloud.py:251: [E1136(unsubscriptable-object), _quick_read_instance_id] Value 'md' is unsubscriptable

This happens here:

cloud-init/cloudinit/sources/DataSourceNoCloud.py

Line 250 in e27c307

if iid_key in md:

and the reason is that load_yaml() can return None, which of course has no membership test and isn't subscriptable:

cloud-init/cloudinit/util.py

Line 840 in e27c307

def load_yaml(blob, default=None, allowed=(dict,)):

One way to fix this by applying this change to

cloud-init/cloudinit/sources/DataSourceNoCloud.py

Line 250 in e27c307

if iid_key in md:

-            if iid_key in md:
+            if md and iid_key in md:
                 return md[iid_key]

And this works, however I wonder if we should make load_yaml() output an empty dict by default instead of None. While it seems a good idea, it may be not because yaml.safe_load("") returns None and we may want to mimic that...

[TheRealFalcon]

I don't think this encoding change is safe to do as a bulk change. I'm guessing that most of these calls will work fine specifying utf-8, but are we sure that every single open is safe?

If I've specified my locale to use ISO-8859, are we sure that none of the files that we're reading will be encoded with ISO-8859 rather than utf-8? If we need to be explicit, then I think locale.getpreferredencoding(False) is the only safe option unless we're sure about every single open call.

For the yaml question, given that our load yaml definition is

def load_yaml(blob, default=None, allowed=(dict,)):

I think it makes sense to keep the default as None and do None checks for what has been returned.

[paride]

I see your point and I'm find dropping the encoding= bulk commit and disable W1514 in pylintrc. We'll have to deal with this at some point, but with more care. +1 on keeping load_yaml() current behavior.

[TheRealFalcon]

Thanks! LGTM assuming CI passes