Review cylc-get-host-metrics function extract_pattern

[kinow]

Describe the bug

Had a look at cylc-get-host-metrics today and noticed a warning in the IDE for the function extract_pattern. Copied below:

def extract_pattern(data_pattern, raw_string):
    """Try to return first parenthesized subgroup of a regex string search."""
    error_msg = "No 're.search' matches for:\n  %s\non the string:\n  %s" % (
        data_pattern.pattern, raw_string)
    try:
        matches = re.search(data_pattern, raw_string)
    except re.error:
        sys.stderr.write(error_msg)
    if matches:
        return matches.groups()
    else:
        raise AttributeError(error_msg)

The issue is that if we reach except re.error, and matches is not set, the next if matches statement would raise a NameError.

However; there is no way for re.error to happen I think. Because a few lines before we have data_pattern.pattern, which means that the data_pattern is not a string, but a compiled regex pattern.

Can't tell whether we should fix and accept string, or ignore the re.error, or just declare match somewhere else... a bit confusing.

Low priority issue, probably will go away with future changes.

Release version(s) and/or repository branch(es) affected?

master and 8.0a1

Steps to reproduce the bug

NA, couldn't write a unit test failing as well, because I think re.error cannot be raised 😕

Expected behavior

I guess type hints either in the comments or signature to indicate what the data_pattern type is, and simplify the code.

Screenshots

Additional context

Pull requests welcome!
This is an Open Source project - please consider contributing a bug fix
yourself (please read CONTRIBUTING.md before starting any work though).

[oliver-sanders]

Closed by #3489