I have a list declared like this -
m_list = own.get("m_list")
Now the problem is I can't access this list from another object. How do I declare the list so that I can access it from another object. I have to check whether or not an element exists.
If you want data to be global in Python, (within a Blender session).
Typically its best to create a module with a unique name specific to your project, import it - and access variables in that module.
Every script which imports the module will be viewing the same data.
In this exact case it sounds like you should add the object it self to a module.
import my_module my_module.my_obj = obj
Some other script
import my_module obj = my_module.my_obj