[TMP, do not merge] adding example for task with FuctionImage

[djarecka]

Acknowledgment

• I acknowledge that this contribution will be available under the Apache 2 license.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Summary

showing example with FunctionalImage as an input - print statements show when the hash value changes

test_5 is the one that failing

Checklist

• All tests passing
• I have added tests to cover my changes
• I have updated documentation (if necessary)
• My code follows the code style of this project
  (we are using black: you can pip install pre-commit,
  run pre-commit install in the pydra directory
  and black will be run automatically with each commit)

[codecov]

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[satra]

this may help track down the issue. while the functionality of an object is preserved through a roundtrip through cloudpickle, the bytestring is not preserved. so if the test that is failing is saving the task to file and loading it, it would likely get a different hash.

In [15]: def func1(a): 
    ...:     return a + 1 
    ...: class foo: 
    ...:     def test(self, b): 
    ...:         return func1(b) 
    ...:                                                                                                

In [16]: ff = foo()                                                                                     

In [17]: sha256(cp.dumps(ff)).hexdigest()                                                               
Out[17]: '9dcd775519701de26beab29199ef7259657c406caf5af36186192a0fa47967d4'

In [18]: sha256(cp.dumps(deepcopy(ff))).hexdigest()                                                     
Out[18]: '9dcd775519701de26beab29199ef7259657c406caf5af36186192a0fa47967d4'

In [19]: sha256(cp.dumps(cp.loads(cp.dumps(ff)))).hexdigest()                                           
Out[19]: 'b85dbb27044c14651596da8eaba9818cfa6351162cc296b2bc1df571891b35c2'

In [20]: ff.test(1)                                                                                     
Out[20]: 2

In [21]: cp.loads(cp.dumps(ff)).test(1)                                                                 
Out[21]: 2

[satra]

indeed, we should not rely on pickle.

you could consider using the __dict__ or __getstate__ of the object if available. or something else about the object. as far as i know there is no generic solution in python for this.

in the short term we could issue exceptions and/or force those tasks to always run.

[satra]

here is a related post (but old - some things in python have changed with 3.x): https://stackoverflow.com/questions/16157835/create-hash-for-arbitrary-objects/

[djarecka]

@satra - I actually did test what happens when I create a deepcopy of this specific object and I was able to get the same hash value.