How can we import python file form one directory to another directory?

Question

I have a framework structure like

Stopper
    /module1
        file1.py
        file2.py
        __init__.py
    /module2
        file3.py
        file4.py
        __init__.py
runner.py
files.py
__init__.py

I want to import class or functions from file3.py to file2.py, as they are different directory. Please let me know how to handle this scenario.

Thanks in advance.