issues: 1947508727

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
1947508727 PR_kwDOAMm_X85dBaso 8322 Implementation of rust based cftime 57914115 open 0     1 2023-10-17T14:00:45Z 2023-10-17T22:20:31Z   CONTRIBUTOR   0 pydata/xarray/pulls/8322

As discussed in #8302, here is a first attempt to implement cftime_rs.

There are a lot of tests and I struggle to understand all the processing in coding/times.py. However, with this first attempt I've been able to make the test_cf_datetime work (ignoring one test)

https://github.com/pydata/xarray/blob/8423f2c47306cc3a4a52990818964f278179491f/xarray/tests/test_coding_times.py#L127-L131

Also there are some key differences betwwen cftime and cftime-rs : - A long int is used to represent the timestamp internally, so cftime-rs will not overflow as soon as numpy, pythonor cftime. It can go from -291,672,107,014 BC to 291,672,107,014 AD approximately and this depends on calendar. - There is no only_use_python_datetimes argument. Instead there are 4 distinct functions : - date2num() - num2date() - num2pydate() - pydate2num() - These functions only take a python list of one dimension and return a list of one dimension. A conversion should be done before. - There is no multiple datetime type (there are hidden) but instead a single object PyCFDatetime - There is no conda repository at the moment

Finally, and regardless of this PR, I guess there could be a speed improvement by vectorizing operations by replacing this : https://github.com/pydata/xarray/blob/df0ddaf2e68a6b033b4e39990d7006dc346fcc8c/xarray/coding/times.py#L622-L649

by something like this :

https://github.com/pydata/xarray/blob/8423f2c47306cc3a4a52990818964f278179491f/xarray/coding/times.py#L631-L670

We can use numpy instead of list comprehensions. It takes a bit more of memory though. 

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