import

When you use import, python first checks sys.modules to see if the module/pkg has been imported already.

If not, it will try to import based on the directories of sys.path.

If import line includes pkg, it will run the __init__.py.
If import line includes module, it will run the whole file.

if yes, it won’t re-run the file no matter it is pkg(__init__.py) or module file.

Let’s say you have the following directory structure:

└── project
    ├── package1
    │   ├── module1.py
    │   └── module2.py
    └── package2
        ├── __init__.py
        ├── module3.py
        ├── module4.py
        └── subpackage1
            └── __init__.py
            └── module5.py

Let’s assume the following:

package1/module2.py contains a function, function1.
package2/__init__.py contains a class, class1.
package2/subpackage1/module5.py contains another function, function2.

from package1 import module1
# There isn’t __init__.py file, so skip it. This will run whole module1.py.

from package1.module2 import function1
# This will run package1(__init__.py) and whole module2.py

from package2 import class1
# This will run package2’s __init__.py

from package2.subpackage1.module5 import function2
# This will skip package2’s __init__.py since it has been imported. It could be verified by sys.modules. It will run subpackage2’s __init__.py and then whole module5.py

name == “main”

Assuming we have files below.

# foo.py
import bar
print("foo.__name__ set to ", __name__)

# bar.py
print("bar.__name__ set to ", __name__)

>>> python bar.py
# Output:
# bar.__name__ set to __main__

>>> python foo.py
# Output:
# bar.__name__ set to bar
# foo.__name__ set to __main__

So if your module is first argument after python, __name__ will be set to __main__. If module ran by import, __name__ is set to module name.

import

__name__ == “__main__”

name == “main”