[Python] How does pickle find modules when loading from a file?

I'm trying to understand how pickling works so that I can correctly design the organization of my repository. Essentially, I pickle objects of type A, whose instances contain objects of type B. A and B are defined in modules in separate packages:

project_dir
|
|-- package_a
|
|-- module_a # class A is defined here
|
|-- package_b
|
|-- module_b # class B is defined here


I did an experiment that I expected to fail, given my knowledge about how pickling works, but it didn't throw an exception:

module_a.py:

class A:
name = "A"


module_b.py:

class B:
def __init__(self) -> None:
self.a = None


In one terminal window:

project_dir> python
>>> import pickle
>>> from package_a.module_a import A
>>> from package_b.module_b import B
>>> b_obj = B()
>>> b_obj.a = A()
>>> b_obj.a.name
'A'
>>> with open("b.pickle", "wb") as f:
... pickle.dump(b_obj, f)
...
>>> exit()


In a new terminal window:

project_dir> python
>>> import pickle
>>> from package_b.module_b import B
>>> with open("b.pickle", "rb") as f:
... b_obj = pickle.load(f)
...
>>> b_obj.a.name
'A'


How is pickle able to construct an A object when I haven't imported module_a anywhere?

EDIT: When I modify A to have a getter for the class name attribute:

class A:
name = "A"

@classmethod
def get_name(cls):
return cls.name


The following experiment still works:

project_dir> python
>>> import pickle
>>> from package_a.module_a import A
>>> from package_b.module_b import B
>>> b_obj = B()
>>> b_obj.a = A()
>>> b_obj.a.get_name()
'A'
>>> b_obj.a.__class__
<class 'package_a.module_a.A'>
>>> with open("b.pickle", "wb") as f:
... pickle.dump(b_obj, f)
...
>>> exit()


>>> import pickle
>>> from package_b.module_b import B
>>> with open("b.pickle", "rb") as f:
... b_obj = pickle.load(f)
...
>>> b_obj.a.get_name()
'A'
>>> b_obj.a.__class__
<class 'package_a.module_a.A'>


This seems contrary to the pickle docs, which state that

...when class instances are pickled, their class’s code and data are not pickled along with them. Only the instance data are pickled.
​

What exactly is going on under the hood here?

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