Improve default behaviour of label_line_ends

[A-CGray]

Purpose

Modifies the behaviour so that if no labels are passed to label_line_ends it will only add labels to lines whose labels don't begin with an underscore. This means label_line_ends will avoid labeling lines that don't have useful labels since matplotlib gives all lines default labels that start with underscores (e.g "_child0").

Example

Previous behaviour:

New behaviour:

Expected time until merged

1 day

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

Checklist

• I have run flake8 and black to make sure the Python code adheres to PEP-8 and is consistently formatted
• I have formatted the Fortran code with fprettify or C/C++ code with clang-format as applicable
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation