[python] warnings

[mglisse]

I just discovered (yes, I should learn python properly...) https://docs.python.org/3/library/warnings.html . That seems like a good fit for print("Warning: computing barycenter of empty diag set. Returns None") in barycenter.py.

[tlacombe]

Noticed. I will do a PR incorporating soon.

[VincentRouvreau]

List of warnings candidates:

• [X] https://github.com/GUDHI/gudhi-devel/blob/6b5b1c0f5d4a1652e668f3ee076ec7fb1b220096/src/python/gudhi/wasserstein/barycenter.py#L59
• [ ] https://github.com/GUDHI/gudhi-devel/blob/6b5b1c0f5d4a1652e668f3ee076ec7fb1b220096/src/python/example/rips_complex_diagram_persistence_from_correlation_matrix_file_example.py#L46-L49
• [ ] https://github.com/GUDHI/gudhi-devel/blob/6b5b1c0f5d4a1652e668f3ee076ec7fb1b220096/src/python/gudhi/representations/metrics.py#L172-L174
• [ ] https://github.com/GUDHI/gudhi-devel/blob/6b5b1c0f5d4a1652e668f3ee076ec7fb1b220096/src/python/gudhi/representations/metrics.py#L179-L181
• [ ] https://github.com/GUDHI/gudhi-devel/blob/6b5b1c0f5d4a1652e668f3ee076ec7fb1b220096/src/python/gudhi/representations/metrics.py#L297-L299
• [ ] https://github.com/GUDHI/gudhi-devel/blob/6b5b1c0f5d4a1652e668f3ee076ec7fb1b220096/src/python/gudhi/representations/metrics.py#L420-L422
• [ ] https://github.com/GUDHI/gudhi-devel/blob/6b5b1c0f5d4a1652e668f3ee076ec7fb1b220096/src/python/gudhi/wasserstein/wasserstein.py#L14-L17
• [ ] https://github.com/GUDHI/gudhi-devel/blob/6b5b1c0f5d4a1652e668f3ee076ec7fb1b220096/src/python/test/test_simplex_tree.py#L548-L553 (TBD if there is some added value to warn in a unitary test)

[mglisse]

As discussed in #1096:

• if we stick to print, it makes sense to at least print to file=sys.stderr.
• in addition to the warnings module, there is also https://docs.python.org/3/library/logging.html , which may be more appropriate for some of the messages (not necessarily all)