isinstance（）因未知原因返回False

Question

So, here is the situation:
I'm using GAE Pipeline lib for the flow, my class FanoutPipeline is derived from Pipeline class from the library:

from pipeline import pipeline
class FanoutPipeline(pipeline.Pipeline):

When the pipeline process is run, it does a check to verify that the object is actually an instance of a class derived from Pipeline, but it returns False:

  yielded = pipeline_iter.send(next_value)
  # here I check that yielded is an object of `FanoutPipeline`
  # class, plz see logs output below
  if isinstance(yielded, Pipeline):  # returns false here

I added a ton of logs to get class tree and their modules:

  import inspect
  logging.debug('Yielded: {}'.format(yielded))
  for cls in inspect.getmro(yielded.__class__):
      logging.debug('Yielded base: {}'.format(inspect.getmodule(cls)))
      logging.debug('Yielded base: {}'.format(cls))
  logging.debug('PipelineMeta classes: {}'.format(_PipelineMeta._all_classes))
  logging.debug('Pipeline: {}'.format(Pipeline))
  logging.debug('Pipeline module: {}'.format(inspect.getmodule(Pipeline)))
  for cls in inspect.getmro(Pipeline):
    logging.debug(inspect.getmodule(cls))
  if isinstance(yielded, Pipeline):

And got the output:

 D 21:55:48.079 Yielded: project.handlers.pipeline_gcm.FanoutPipeline(*(None, {u'campaign_id': u'xxx', u'campaign_name': u'xmas notification', u'execution': {u'action': u'market', u'conditions': {u'delayBetweenNotificationsHours': 0, u'in... (515 bytes), **{}) D 21:55:48.079 Yielded base: <module 'project.handlers.pipeline_gcm' from '/base/data/home/apps/s~project-dev3/9.389913797024223872/projects/handlers/pipeline_gcm.pyc'> D 21:55:48.079 Yielded base: <class 'project.handlers.pipeline_gcm.FanoutPipeline'> D 21:55:48.080 Yielded base: <module 'pipeline.pipeline' from '/base/data/home/apps/s~project-dev3/9.389913797024223872/libraries/pipeline/pipeline.pyc'> D 21:55:48.080 Yielded base: <class 'pipeline.pipeline.Pipeline'> D 21:55:48.080 Yielded base: <module '__builtin__' (built-in)> D 21:55:48.080 Yielded base: <type 'object'> D 21:55:48.081 PipelineMeta classes: [<class 'libraries.pipeline.pipeline.Pipeline'>] D 21:55:48.081 Pipeline: <class 'libraries.pipeline.pipeline.Pipeline'> D 21:55:48.081 Pipeline module: <module 'libraries.pipeline.pipeline' from '/base/data/home/apps/s~project-dev3/9.389913797024223872/libraries/pipeline/pipeline.pyc'> D 21:55:48.082 <module 'libraries.pipeline.pipeline' from '/base/data/home/apps/s~project-dev3/9.389913797024223872/libraries/pipeline/pipeline.pyc'> D 21:55:48.082 <module '__builtin__' (built-in)> 

As you see, yielded has clearly pipeline.pipeline.Pipeline in base classes, the module paths match.

Here are some ideas why it could happen: 1. The object is passed somehow between processes, and the check fails since one base class is loaded in one process, the other - in the other. 2. There is a difference of relative paths, ie pipeline.pipeline module in process where object is created
and libraries.pipeline.pipeline in the process where it's used and the isinstance check is being done.

Could you please help me with this issue? What should I try in the first place? What could be the reason to this failure?

Answer 1

You are importing two versions of the class, one as libraries.pipeline.pipeline.Pipeline and another as pipeline.pipeline.Pipeline . That would mean you have both /base/data/home/apps/s~project-dev3/9.389913797024223872/ and /base/data/home/apps/s~project-dev3/9.389913797024223872/libraries in sys.path . Although you know they are just two paths to the same module, python doesn't know that and treats them as two different classes.

You'll need to decide whether you want to base your imports on libraries or the various modules inside libraries and then write your imports consistently. You should also stop adding the "unchosen" directory to sys.path so that importing the module in the wrong way, fails.