Add dummy beam wrapper

[Eshan-Agarwal]

Fix #1946

[Eshan-Agarwal]

@Conchylicultor Please have a look on changes.

[vijayphoenix]

You can consider making these changes just for now.
However, after #1947 is merged, I think it would be best to inherit FakeModule rather than ModuleType.
It will avoid duplication of code

[vijayphoenix]

Define __getattr__ instead of __getattribute__.

[Eshan-Agarwal]

__getattr__ make some trouble here because we want DoFn to call with DummyBeam so if use getattr here this will executing without any errors here, the reason why I am using __getattribute__ is __getattribute__ calls no matter what unlike getattr

[vijayphoenix]

I don't think we should throw an error when DoFn is accessed.

If beam isn't found, then the imports works, but calling SomeFn(), some_ptransform_fn(),... raise the lazy import error ('Please install appache_beam')

We don't want this to happen. So, we should not throw any errors when members of DummyBeam are accessed.

However, proceed only after consulting @Conchylicultor.
(Just in case I am wrong 😅)

[Eshan-Agarwal]

Beam API have DoFn and pipiline but it dont have SomeFn its just name i think thats why it inherit beam.DoFn so i think it is good to get error when invoking beam.DoFn 🙂

[Conchylicultor]

@vijayphoenix is right. The all point of this module is to allow using beam without raising error when declaring the beam functions. However error should be raised when the functions are called.

[Eshan-Agarwal]

Thanks but this won't works 🙂

[Eshan-Agarwal]

However I found a way to do this using __new__ in Empty class and its working, when I call SomeFn() it raises error, is it necessary to use types.ModuleType ?

[Conchylicultor]

You shouldn't have to use __new__. __init__ should be enough.

What is the issue with types.ModuleType ?

[Conchylicultor]

Modules should inherit from ModuleType, but not other Class or functions.

class EmptyClass(object):
  def __init__(self):
    raise ...

[Eshan-Agarwal]

okay then doing in this way ?

class Empty(object):
   
    def __init__(self, *args, **kwargs):
        err_msg = _MSG.format(name="apache_beam")
        raise ImportError(err_msg)
        
    
class DummyBeam(types.ModuleType):

    DoFn = Empty
    Pipeline = Empty
    ptransform = Empty

    def __init__(self):
        return None

what is use of types.ModuleType here ?

[Conchylicultor]

Only add the with self.assertRaisesWithPredicateMatch(ImportError, _err_msg): around the line which actually raise the exception.
Otherwise I don't know where the exception is coming from.

[Conchylicultor]

Creating the class should works, which is the entire point.
but instantiated the class should fail.:

class SomeDoFn(beam.DoFn):  # Works
  pass

with self.assertRaisesRegex(...):
  SomeDoFn()  # Raise error

[Conchylicultor]

@vijayphoenix is right. The all point of this module is to allow using beam without raising error when declaring the beam functions. However error should be raised when the functions are called.