Questions about the import ordering

[ChrisWang]

Dear all,

I am reading the book "Core Python Programming". In the chapter talking about modules, it says the modules should follow this ordering:

import Python Standard Library modules
 
import Python third party modules
 
import Application-specific modules

I am not sure whether the ordering will impact the module's loading or search efficiency. For example, a common module in the standard library can be free from being imported several times, if this module will be imported by application-specific modules.

test.py

#test.py
import os
import MyModuleA
import MyModuleB
...
 

MyModuleA.py

#MyModuleA.py
import os
...
 

MyModuleB.py

#MyModuleB.py
import os
...
 

If we follow the ordering to import the modules, here we import standard library "os", we may save some time, right? It's only my assumption and I am not sure I am right. But I am curious to know whether there are some benefits we can get from the this ordering.

Could anyone be kind enough to give me the answer? Thanks a lot.

Have a nice holiday!

[bvdet]

A module is imported and executed only once. A subsequent import of the same module only creates a reference to the module namespace created on the previous import.

The ordering of the imports is primarily for consistency and is recommended in PEP 8. I don't know if there are any performance benefits.

-BV

[ChrisWang]

@bvdet
Thanks BV. Could you please show me detailed explanation about the consistency?
I've read the description about imports in PEP08, but I think I am still puzzled about that.

[bvdet]

ChrisWang,

Sorry, I have no detailed explanation. I think the reference to consistency is referring to Python applications in general.

If a top level module imports a required Python library module and another application specific module is imported and executed and it imports the same Python library module, a reference is made to the module instead of it being importing again. If you think about it, it makes sense to order the imports that way.

I would not import a module unless the current module requires it.

-BV

[ChrisWang]

Ok. Thank you very much.

Have a great holiday!