[FIX] Timeseries: time_variable now created in Timeseries

[jerneju]

Issue

Some widgets (Seasonal Adjustment, Moving Transform, and Difference) create Timeseries when they get Table and they do not set time_variable.

Description of changes

Scripting part which creates time_variable is now moved from widget As Timeseries to Timeseries.
Now this code can be used when creating Timeseries from Table.

Includes

• Code changes
• Tests
• Documentation

[kernc]

I don't think any ContinuousVariable will cut it.

[kernc]

I don't like this. Where does it happen?

[codecov-io]

Codecov Report

Merging #33 into master will decrease coverage by 0.42%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##           master      #33      +/-   ##
==========================================
- Coverage   55.88%   55.45%   -0.43%     
==========================================
  Files           7        7              
  Lines         646      651       +5     
  Branches       99      101       +2     
==========================================
  Hits          361      361              
- Misses        249      253       +4     
- Partials       36       37       +1

Impacted Files	Coverage Δ
orangecontrib/timeseries/timeseries.py	75.8% <0%> (-6.65%)	⬇️
orangecontrib/timeseries/functions.py	61.18% <50%> (ø)	⬆️

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[jerneju]

https://sentry.io/biolab/orange3-timeseries/issues/277426278/

[jerneju]

https://sentry.io/biolab/orange3-timeseries/issues/420934579/

[kernc]

I don't like this change. .time_variable can be None. The failure happens on https://github.com/biolab/orange3-timeseries/pull/33/files#diff-baa207cfea1077bb261faf9efcf809c8R93. How about if the assertion assert var in self.domain was changed to:

if var is None:
    self.attributes = self.attributes.copy()
    self.attributes.pop('time_variable')
    return

assert var in self.domain

Would that work?

[jerneju]

@kernc : And you also do not want to have a conversion from Table to Timeseries in a scripting part?

[kernc]

Why, doesn't Timeseries.from_data_table(table) do that?

[kernc]

This looks safer to me. Thanks.