Question

When you import a module, then reimport it again, will it get reimported/overwritten, or skipped?
When you import module “a” and “b”, but also have module “b” imported in module “a”, what happens? Is it safe to do this? For example if that module “b” has a class instantiated in it, will you end up instantiating it twice?

Answer 1

import loads the matching .py, .pyc or .pyo file, creates a module object, and stores it with its fully qualified (“dotted”) name in the sys.modules dictionary. If a second import finds the module to import in this dictionary, it will return it without loading the file again.

To answer your questions:

When you import a module, then reimport it again, will it get reimported/overwritten, or skipped?

It will get skipped. To explicitely re-import a module, use the reload() built-in function.

When you import module “a” and “b”, but also have module “b” imported in module “a”, what happens?

import a will load a from a.py[c], import b will return the module sys.modules['b'] already loaded by a.

Is it safe to do this?

Yes, absolutely.

For example if that module “b” has a class instantiated in it, will you end up instantiating it twice?

Nope.