Issue 2378: Remove unicode string form in rdflib/term.py

[ajnelson-nist]

Summary of changes

This PR updates some docstrings to no longer use the Python 2 unicode string pattern (u"some string").

This PR is scoped to the original file where I'd encountered the problem, running python3 -m doctest rdflib/term.py.

One outstanding doctest issue remains, but rather than attempt to fix everything, this PR is filed now to make incremental progress, and trial the goal progression laid out in #2383.

The last issue for rdflib/term.py, which I think someone else will need to file a PR for, is evidenced in this shell transcript:

$ python3 -m doctest rdflib/term.py
**********************************************************************
File "/private/tmp/rdflib/rdflib/term.py", line 677, in term.Literal
Failed example:
    Literal(1) > URIRef('foo') # by node-type
Exception raised:
    Traceback (most recent call last):
      File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.9/lib/python3.9/doctest.py", line 1336, in __run
        exec(compile(example.source, filename, "single",
      File "<doctest term.Literal[19]>", line 1, in <module>
        Literal(1) > URIRef('foo') # by node-type
    TypeError: '>' not supported between instances of 'Literal' and 'URIRef'
Failed to convert Literal lexical form to value. Datatype=http://www.w3.org/2001/XMLSchema#integer, Converter=<class 'int'>
Traceback (most recent call last):
  File "/private/tmp/rdflib/rdflib/term.py", line 2084, in _castLexicalToPython
    return conv_func(lexical)  # type: ignore[arg-type]
ValueError: invalid literal for int() with base 10: 'a'
**********************************************************************
1 items had failures:
   1 of  21 in term.Literal
***Test Failed*** 1 failures.

Checklist

• Checked that there aren't other open pull requests for
  the same change.
• Added tests for any changes that have a runtime impact. (N/A)
• Checked that all tests and type checking passes. (Pending CI results, all tests pass in main, and more tests pass in the "Goal" branch)
• For changes that have a potential impact on users of this project:
  • Updated relevant documentation to avoid inaccuracies. (N/A)
  • Considered adding additional documentation. (N/A)
  • Considered adding an example in ./examples for new features. (N/A)
  • Considered updating our changelog (CHANGELOG.md).
• Considered granting push permissions to the PR branch,
  so maintainers can fix minor issues and keep your PR up to date.

[ajnelson-nist]

I'm not sure why something went awry for only Python 3.11. After I worked through documenting #2385, I was able to get this log output:

================================================== FAILURES ===================================================
______________________________________ test_guess_format_for_parse[None] ______________________________________
Traceback (most recent call last):
  File "/private/tmp/rdflib/rdflib/plugin.py", line 137, in get
    p: Plugin[PluginT] = _plugins[(name, kind)]
                         ~~~~~~~~^^^^^^^^^^^^^^
KeyError: ('text/plain', <class 'rdflib.parser.Parser'>)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/private/tmp/rdflib/test/test_graph/test_graph.py", line 347, in test_guess_format_for_parse
    graph.parse(location="http://www.w3.org/ns/adms.ttl")
  File "/private/tmp/rdflib/rdflib/graph.py", line 1489, in parse
    parser = plugin.get(format, Parser)()
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/private/tmp/rdflib/rdflib/plugin.py", line 139, in get
    raise PluginException("No plugin registered for (%s, %s)" % (name, kind))
rdflib.plugin.PluginException: No plugin registered for (text/plain, <class 'rdflib.parser.Parser'>)
-------------------------------------------- Captured stderr call ---------------------------------------------
127.0.0.1 - - [12/May/2023 11:36:40] "GET /file/4b5b7d9e0d9c4cbaafda954b640dd450 HTTP/1.1" 200 -

It seems this is unrelated enough to this PR that it's not a blocking issue, but this might be a heads-up that CI is going to complain the next time someone pushes to main.

[ghost]

I'm not sure why something went awry for only Python 3.11.
...
It seems this is unrelated enough to this PR that it's not a blocking issue, but this might be a heads-up that CI is going to complain the next time someone pushes to main.

fwiw I can confirm it's unrelated to this PR, aucampia is already working to resolve the issue: #2382

[coveralls]

Coverage: 90.85%. Remained the same when pulling 55f4906 on ajnelson-nist:issue-2378-rdflib-term-ustrings into fec7f0a on RDFLib:main.

[aucampia]

Thanks for the PR, looks good to me.