Replace VarName with built-in str

[osyuksel]

Description

This change:

• Replaces VarName type with built-in str
• Updates get_var_name to have it work without getattr

Related Issue

• Closes Remove VarName from codebase #7843
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

---

📚 Documentation preview 📚: https://pymc--7855.org.readthedocs.build/en/7855/

[osyuksel]

I also attempted to address the second point re. getattr(variable, "name") in the issue with this commit, however, making an explicit attribute reference (i.e. calling var.name instead of getattr) causes the tests to fail, so I assume there must be some variables where the attribute is not present.

==================================== ERRORS ====================================
__________________ ERROR collecting tests/test_model_graph.py __________________
tests/test_model_graph.py:467: in <module>
    class TestVariableSelection:
tests/test_model_graph.py:499: in TestVariableSelection
    ModelGraph(model_with_different_descendants()).vars_to_plot(),
pymc/model_graph.py:238: in __init__
    self._all_var_names = get_default_varnames(self.model.named_vars, include_transformed=False)
pymc/util.py:212: in get_default_varnames
    return [var for var in var_iterator if not is_transformed_name(get_var_name(var))]
pymc/util.py:217: in get_var_name
    return str(var.name if var.name is not None else var)
E   AttributeError: 'str' object has no attribute 'name'

[ricardoV94]

That should check explicitly if the input is a string, instead of trying to call var.name on it

[osyuksel]

Makes sense, missed that var could be str. Updated PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.65%. Comparing base (dc7cfee) to head (afcc142).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7855      +/-   ##
==========================================
+ Coverage   88.25%   91.65%   +3.40%     
==========================================
  Files         116      116              
  Lines       18845    18844       -1     
==========================================
+ Hits        16631    17272     +641     
+ Misses       2214     1572     -642     

Files with missing lines	Coverage Δ
pymc/model/core.py	93.38% <100.00%> (ø)
pymc/model_graph.py	84.48% <100.00%> (ø)
pymc/util.py	81.11% <100.00%> (-0.09%)	⬇️

... and 4 files with indirect coverage changes

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