Timestamped experiments

[brosaplanella]

Description

Enable functionality to "timestamp" experiment steps so they only get triggered at that date & time. At the moment the timestamps can be defined as:

• "Day D HH:MM:SS"
• "YYYY-MM-DD HH:MM:SS"

I am using the datetime package so the flexibility with the format (e.g. padding zeros) is that of datetime.

Fixes #1839

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ flake8
• All tests pass: $ python run-tests.py --unit
• The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (997b758) 99.71% compared to head (f641985) 99.71%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2616   +/-   ##
========================================
  Coverage    99.71%   99.71%           
========================================
  Files          248      248           
  Lines        18683    18736   +53     
========================================
+ Hits         18629    18682   +53     
  Misses          54       54           

Impacted Files	Coverage Δ
pybamm/experiment/experiment.py	100.00% <100.00%> (ø)
pybamm/simulation.py	100.00% <100.00%> (ø)
pybamm/solvers/solution.py	100.00% <100.00%> (ø)
pybamm/step/_steps_util.py	100.00% <100.00%> (ø)

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[brosaplanella]

@tinosulzer, following #2960, do we want the tags to be in the string or just as an option in _Step? I guess the latter, but just wanted to double check before undoing some of the changes.

[valentinsulzer]

I think just an option. I made it so you can pass a single tag or a list of tags

[brosaplanella]

I think this is ready to review

[rtimms]

How come we need a separate model for this? Can't we use the current model and set the current to be zero like we do for a rest?

[brosaplanella]

I thought it would be more robust to have a separate model for rest, in case the user only has, for example, power driven steps (unlikely, I know).

[rtimms]

ah ok, yeah, makes sense

[rtimms]

looks good, thanks @brosaplanella !

[valentinsulzer]

Functionality looks good. In terms of API I am wondering whether timestamp is the best name (what about start_time?). Also wondering whether we should just always require a datetime object, instead of providing support for some (but not all) datetime formats. It's not too much work for someone to write their own function to create a datetime object from a string.

[brosaplanella]

Functionality looks good. In terms of API I am wondering whether timestamp is the best name (what about start_time?).

We could call it start_time (I agree, I think it is clearer) and then the other variables could be next_start_time and end_time. That would make everything clearer I think.

Also wondering whether we should just always require a datetime object, instead of providing support for some (but not all) datetime formats. It's not too much work for someone to write their own function to create a datetime object from a string.

Currently what we do is process the string by using datetime.strptime (https://www.digitalocean.com/community/tutorials/python-string-to-datetime-strptime) so we could push this on the user's side. In any case, if later we want to support string it is way easier to add it at a later stage than include it now and remove it later.

Will make these changes and then I will merge.