Find or create an instrument without worrying about existing instances

[astafan8]

This new function find_or_create_instrument avoids the hassle of usage of Instrument.find_instrument. In case an instrument does not already exist, the latter will throw an exception, while the new function will just return the reference to that instrument.

If this function is used to create instruments, then it can be reexecuted, because unlike find_instrument or just reinstantiation with a constructor, this function does not throw. Moreover, thanks to the recreate kwarg, it allows to recreate an instance of the instrument in case one already exists.

Researchers find this convenience function very handy. pytopo repository (Delft lab) also has a variation of this convenience function. Even I ended up implementing this function for v0_characterization experiment and repository.

@wpfff Let me know if this is good enough (I've decided to avoid the force_new_instance feature). Update: aligned on the solution.

[codecov]

Codecov Report

Merging #1210 into master will increase coverage by 0.23%.
The diff coverage is 95.23%.

@@            Coverage Diff             @@
##           master    #1210      +/-   ##
==========================================
+ Coverage   80.53%   80.76%   +0.23%     
==========================================
  Files          49       49              
  Lines        6821     6841      +20     
==========================================
+ Hits         5493     5525      +32     
+ Misses       1328     1316      -12

[jenshnielsen]

Looks good to me. Could consider documenting and or testing what happens if an instrument of the same name but a different class exists. As far a I can see that will raise a TypeError inside find_instrument

[WilliamHPNielsen]

Looks good to me.

[astafan8]

just added a test and a note about "same name, different class" case. If necessary, the current behavior can be revisited later.