pasoroki / singleton_tests

Example repo that shows how to mess up with importing

singleton_tests

Example repo that shows how to mess up with importing in python. Key things:

• sys.path is shared across all scrip parts. If changed in one file, other files are influenced
• importing module with different path loads it under different name in module cache
• Singleton instances (well, anything) are part of the loaded module data, so could be duplicated

Details

main script imports both proxy library and helloworld module When module_helloworld.py is loaded, it mess up with sys.path. Adds proxis folder.

Such action affects main script. Now it is able to load proxy library using both ways:

• from proxy_lib import ProxySingleton
• from proxies.proxy_lib import ProxySingleton

Both will work, but each will be saved in module cache under different name. Any could be safely used while its name in consistence with other imports (in module_helloworld.py).

The main_good.py covers same module import name (proxies.proxy_lib and proxies.proxy_lib) The main_bad.py covers different module import name (proxies.proxy_lib and proxy_lib)

In the outputs of the commands you can see that sys.modules will contain different results and singleton behavior as well as id will be different

As an extra, main.py contains execution of the get_fake_module method that will load module code into different module object that also show that objects will be different