[FIX] File: Disallow changing string columns to datetime

[jerneju]

Issue

ValueError - could not convert string to float: '02.02.17'
https://sentry.io/biolab/orange3/issues/196743724/

Description of changes

Datetime option only if numerical.

Includes

• Code changes
• Tests
• Documentation

[codecov-io]

Codecov Report

Merging #2050 into master will decrease coverage by -1.04%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #2050      +/-   ##
==========================================
- Coverage    70.7%   69.66%   -1.04%     
==========================================
  Files         315      315              
  Lines       53903    53903              
==========================================
- Hits        38111    37554     -557     
- Misses      15792    16349     +557

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[jerneju]

https://sentry.io/biolab/orange3/issues/198615964/

[jerneju]

#1520, #1798

[ajdapretnar]

This fixes the error nicely, but I was wondering whether we could provide the user with a better error message. Perhaps "Use ISO format for datetime variables (e.g. 2017-02-27)"? Say in a form of a warning? Just to tell the user how to proceed with datetime variables? :)

[jerneju]

ISO 8601? Yes, program knows how to read "2017-03-01" but have no clue what means "2017-03-01T12:49:39+00:00" ("could not convert string to float").

[ajdapretnar]

Complain to @kernc. It does work with 2017-03-01 12:49:39 though.
Can we come up with a good user message?

[jerneju]

Great, I see it does work with that kind of format. I changed the code in a way that a user message won't be necessary. Now only variables which can be set to numerical can also be set to datetime.

[astaric]

While eventually we would prefer to allow user to specify the datetime format that would be able to parse the strings, this fix should prevent crashes in the mean time.

If possible, please add a test for the fix as well.

[astaric]

IMHO, this would be much clearer if written like:

if no_numeric:
  # Do not allow selection of numeric and datetime
  items = [i for i in self.items if i not in ("numeric", "datetime")]
else:
  items = self.items

ind = items.index(index.data())
combo.addItems(items)
combo.setCurrentIndex(ind)

[astaric]

Could you include a test?

[kernc]

From the top of the head, the reason it didn't work with:

2017-03-01T12:49:39+00:00

is that the colon in the timezone part doesn't parse with datetime.strptime. Standards-wise, I guess we deviate a little.