pending deprecations

[mathause]

in xarray we get some deprecation warnings that stem from pseudonetcdf.

• "rU" read mode:

 /usr/share/miniconda/envs/xarray-tests/lib/python3.8/site-packages/PseudoNetCDF/icarttfiles/ffi1001.py:95:
DeprecationWarning: 'U' mode is deprecated
    f = openf(path, 'rU', encoding=encoding)

there are several uses of "rU" those, e.g.:

pseudonetcdf/src/PseudoNetCDF/icarttfiles/ffi1001.py

Lines 65 to 66 in ddfa0c4

	ffifmt = openf(
	path, 'rU', encoding='utf-8').readline().strip()[-4:]

The suggestion seems to be to just use "r" (https://stackoverflow.com/questions/56791545/what-is-the-non-deprecated-version-of-open-u-mode)

• Time tuple will be replaced by datetime and dateutil

../../../../../usr/share/miniconda/envs/xarray-tests/lib/python3.8/site-packages/PseudoNetCDF/camxfiles/timetuple.py:18
  /usr/share/miniconda/envs/xarray-tests/lib/python3.8/site-packages/PseudoNetCDF/camxfiles/timetuple.py:18: PendingDeprecationWarning: Time tuple will be replaced by datetime and dateutil
    warn(PendingDeprecationWarning(

I don't think it's urgent, just wanted to mention it here. xref pydata/xarray#3266

[barronh]

Thanks for the heads up! I'll fix these.

[barronh]

The rU has been changed to r in PR #116. timetuple should still be addressed.