How to exit a module before it has finished parsing?

Question

I have a module that imports a module, but in some cases the module being imported may not exist. After the module is imported there is a class inherits from a class the imported module. If I was to catch the ImportError exception in the case the module doesn't exist, how can I stop Python from parsing the rest of the module? I'm open to other solutions if that's not possible.

Here is a basic example (selfaware.py):

try:
    from skynet import SkyNet
except ImportError:
    class SelfAwareSkyNet():
        pass
    exit_module_parsing_here()

class SelfAwareSkyNet(SkyNet):
    pass

The only ways I can think to do this is:

• Before importing the selfaware.py module, check if the skynet module is available, and simply pass or create a stub class. This will cause DRY if selfaware.py is imported multiple times.

• Within selfaware.py have the class defined withing the try block. e.g.:

  try:
      from skynet import SkyNet
      class SelfAwareSkyNet(SkyNet):
          pass
  except ImportError:
      class SelfAwareSkyNet():
          pass
  

Answer 1

You could use:

try:
   from skynet import SkyNet
   inherit_from = SkyNet
except ImportError:
   inherit_from = object

class SelfAwareSkyeNet(inherit_from):
    pass

This works only if the implementation do not differ.

Edit: New solution after comment.

Answer 2

This should do the trick:

try:
    from skynet import SkyNet
except ImportError:
    class SelfAwareSkyNet():
        pass
else:
    class SelfAwareSkyNet(SkyNet):
        pass

Answer 3

try: supports an else: clause

try:
    from skynet import SkyNet

except ImportError:
    class SelfAwareSkyNet():
        pass

else:
    class SelfAwareSkyNet(SkyNet):
        pass

Answer 4

Most simple solution:

try:
    from skynet import SkyNet
    parent = SkyNet
except ImportError:
    parent = object

class SelfAwareSkyNet(parent):
    pass

Note: Untested but you get the idea.