matplotlib / basemap

six version 1.16 was released 2021-05-05: https://github.com/benjaminp/six/releases/tag/1.16.0

The basemap package does not permit this version:

basemap/packages/basemap/requirements.txt

six >= 1.10, < 1.16

Is there a reason this version is incompatible, or can the requirements.txt be updated to allow it?

As far as I know, there should be no incompatibilities. I normally set upper pins just as a precaution, i.e. to be sure that a possible broken release in the dependencies is not propagated to the library (when installing).

In this case with six, I just forgot to increase the upper pin at some point, but it should be safe to increase it (six is quite reliable, e.g. it defines python_requires properly).

I was reviewing a bit further, and in fact six is only used inside the basemap.cm module to import iteritems:

basemap/packages/basemap/src/mpl_toolkits/basemap/cm.py

Line 16 in c4805e3

from six import iteritems

Later, this iteritems is used to loop over the contents of the colormap dictionaries stored in the same file. Based on how small these dictionaries are, I think that it could be possible to simply use dict.items below and remove the dependency on six:

basemap/packages/basemap/src/mpl_toolkits/basemap/cm.py

Line 77 in c4805e3

for key,val in iteritems(data):

@iamthad After some minor refactoring of matplotlib.cm, the six module is not required anymore as a dependency. Therefore, in the next patch release basemap will not be limiting other packages that try to install the newer six version.

six 1.16 is not permitted