Try deepcopy combine_fn and fallback to pickling if TypeError.

[claudevdm]

Roll forward with #32598 + fix the copy behavior if a module is being copied.

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[tvalentyn]

If we:

1. replace this line with
   self._combine_fn_copy = pickler.loads(pickler.dumps(combine_fn))

2. use cloudpickle pickler

will we still hit https://github.com/apache/beam/issues/26209 ?

[claudevdm]

No. The pickler.loads(pickler.dumps(a)) creates a deep copy of the instance a. For example

from apache_beam.internal import cloudpickle_pickler
class TestClass:   
def __init__(self):
     self._setup_called = False
     
   def setup(self, *args, **kwargs):
     assert not self._setup_called, 'setup should not be called twice'
     self._setup_called = True

>>> original = TestClass()
>>> pickled_a = cloudpickle_pickler.loads(cloudpickle_pickler.dumps(original))
>>> pickled_b = cloudpickle_pickler.loads(cloudpickle_pickler.dumps(original))
>>> pickled_a == pickled_b
False
>>> pickled_a.setup()
>>> pickled_a._setup_called
True
>>> pickled_b.setup()
>>> pickled_a.setup()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 7, in setup
AssertionError: setup should not be called twice

[claudevdm]

I can write a unit test for this scenario too

[tvalentyn]

    except TypeError as e:

Can there be other errors? Let's catch all exceptions.

          'Failed to copy combine function. Ensure python dependencies are'

          ' properly set up: %s'

I thought whether we should surface this, and I think this might create unactionable noise for the users. I wouldn't print anything if the copy, or copy via pickle was successful.