[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:

• gudhi-devel/src/python/gudhi/wasserstein/barycenter.py

  Line 59 in 6b5b1c0

  print("Warning: computing barycenter of empty diag set. Returns None")

• gudhi-devel/src/python/example/rips_complex_diagram_persistence_from_correlation_matrix_file_example.py

  Lines 46 to 49 in 6b5b1c0

  	print("#####################################################################")
  	print("Caution: as persistence diagrams points will be under the diagonal,")
  	print("bottleneck distance and persistence graphical tool will not work")
  	print("properly, this is a known issue.")

• gudhi-devel/src/python/gudhi/representations/metrics.py

  Lines 172 to 174 in 6b5b1c0

  	except ImportError:
  	print("Gudhi built without CGAL")
  	raise

• gudhi-devel/src/python/gudhi/representations/metrics.py

  Lines 179 to 181 in 6b5b1c0

  	except ImportError:
  	print("POT (Python Optimal Transport) is not installed. Please install POT or use metric='wasserstein' or metric='hera_wasserstein'")
  	raise

• gudhi-devel/src/python/gudhi/representations/metrics.py

  Lines 297 to 299 in 6b5b1c0

  	except ImportError:
  	print("Gudhi built without CGAL")
  	raise

• gudhi-devel/src/python/gudhi/representations/metrics.py

  Lines 420 to 422 in 6b5b1c0

  	except ImportError:
  	print("POT (Python Optimal Transport) is not installed. Please install POT or use mode='hera'")
  	raise

• gudhi-devel/src/python/gudhi/wasserstein/wasserstein.py

  Lines 14 to 17 in 6b5b1c0

  	try:
  	import ot
  	except ImportError:
  	print("POT (Python Optimal Transport) package is not installed. Try to run $ conda install -c conda-forge pot ; or $ pip install POT")

• gudhi-devel/src/python/test/test_simplex_tree.py

  Lines 548 to 553 in 6b5b1c0

  	try:
  	from scipy.sparse import coo_matrix
  	from scipy.spatial import cKDTree
  	except ImportError:
  	print("Skipping, no SciPy")
  	return

  (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)