Python: Does importing "sys" module also import "os" module?

I am following this tutorial to see why Python doesn’t recognize an environment variable that was set at the Conda prompt (using CMD syntax, as this is an Anaconda installation on Windows 10).

It requires the os module, and as part of my getting familiar with Python, I decided to test whether os was already imported. Testing the presence of a module requires the sys module (as described here).

Strangely, right after importing sys, I found that os was imported without me having to do so. I find this odd, as most of my googling shows that you have to import them individually, e.g., here.

Does importing sys also impart os, as it seems to? If so, why is it common to import both individually?

I can’t test for the presence of os before importing sys, as I need sys to test for the presence of modules.

Here is the code that shows the apparent presence of os from importing sys, formatted for readability. It starts from the Conda prompt in Windows. The Conda environment is "py39", which is for Python 3.9:

(py39) C:\Users\User.Name > python

   Python 3.9.16 (main, Mar  8 2023, 10:39:24)
   [MSC v.1916 64 bit (AMD64)] on win32

   Type "help", "copyright", "credits" or "license"
   for more information.

>>> import sys

>>> "os" in sys.modules

   True

Afternote: Thanks to Zero’s answer, I found this code to be more what I’m looking for. After loading sys, the appropriate test is ( 'os' in sys.modules ) and ( 'os' in dir() ):

(py39) C:\Users\User.Name > python
'os' in dir() # False

import sys
'os' in sys.modules , 'os' in dir() # (True, False)
( 'os' in sys.modules ) and ( 'os' in dir() ) # False

import os
'os' in sys.modules , 'os' in dir() # (True, True)
( 'os' in sys.modules ) and ( 'os' in dir() ) # True

sys.modules shows whether the module has been imported anywhere (presumably in the code that the Python interpreter has executed) while dir() indicates whether the module name is in the current namespace. Thanks to Carcigenicate for clarifying this point, and I hope that I understood it properly.

>Solution :

sys uses the os module, but doesn’t import it to your code. You can confirm it through the code.

In [1]: import sys

In [2]: os.getcwd()
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Cell In [2], line 1
----> 1 os.getcwd()

NameError: name 'os' is not defined