Cyclic dependency within isodatetime

[kinow]

Running pydeps against Cylc master, without filtering out dependencies, I noticed that it reported zero cyclic dependency for Cylc, but one for isodatetime.

Executing pydeps --show-cycles isodatetime against latest version in master for isodatetime reports:

This is because (1) isodatetime.data depends on the (2) cylc.dumpers. (2) isodatetime.dumper's depends on the (3) isodatetime.parsers (this dependency is imported only in get_time_zone). And (3) isodatetime.parsers depends on (1) isodatetime.data.

This normally indicates that the design of the dependency between classes/categories can be simplified. Allowing easier maintenance (e.g. refactor, move classes to different packages, and so on).

[matthewrmshin]

Yes. We can do with a good refactor here. I believe we should rearrange the modules so we have a module for each of:

• Duration (and its parser and dumper).
• Calendar.
• TimePoint (and its parser and dumper).
• TimeRecurrence (and its parser and dumper).