How do imports work in Spyder IDE? Why is it different to running your code from Powershell?

Question

I have seen a lot of questions on this topic, but None seem to explain why this is happening or provide a solution I can use.

The following script gives 8 different outputs depending on where it's run from and I really don't understand why. I've managed to pin down a pattern but still don't understand why this occurs and it hasn't helped me solve the problem.

I have a file called

__init__.py

In the same directory as this file, I have a folder called "source_code". In that folder I have another file called

__init__.py

The

source_code/__init__.py

file contains one line of code which is:

print("source_code imported")

The first

__init__.py

file has the following script:

import sys

print(sys.executable)
print(sys.path[0])

try:
    from . import source_code
except ImportError as ie:
    print(ie)
    
try:
    import source_code
except ImportError as ie:
    print(ie)

I am using Spyder 4.1.5 as part of the Anaconda package, as well as Powershell on Windows 10. I have a virtual environment, created with conda, with only Jupyter notebook and spider installed.

The pattern I have found (as far as I can tell) is as follows:

1. If I run the script through powershell, from outside the virtual environment, the output is as follows:

C:\Users\user\Desktop\Anaconda\python.exe
C:\Users\user\path\to\file
cannot import name 'source_code' from '__main__' (.\path\to\file\__init__.py)
source_code imported

2. if I run through Powershell from inside the virtual environment, the output is:

C:\Users\user\Desktop\Anaconda\envs\venv\python.exe
C:\Users\user\path\to\file
attempted relative import with no known parent package
source_code imported

3. if I open spyder, outside the virtual environment, and run the script by clicking into the editor and pressing "Control+Enter", the output is:

C:\Users\user\Desktop\Anaconda\python.exe
C:\Users\user\Desktop\Anaconda\python37.zip
cannot import name 'source_code' from '__main__' (C:\Users\user\path\to\file\__init__.py)
No module named 'source_code'

4. If (still in spyder, outside the virtual environment) I click on the run button in the bar at the top, the output is:

C:\Users\user\Desktop\Anaconda\python.exe
C:\Users\user\Desktop\Anaconda\python37.zip
cannot import name 'source_code' from '__main__' (C:\Users\user\path\to\file\__init__.py)
source_code imported

5. If I then click back into the editor and press "Control+Enter" again, the output is now:

C:\Users\user\Desktop\Anaconda\python.exe
C:\Users\user\Desktop\Anaconda\python37.zip

6. If I run spyder from inside the virtual environment. Click into the editor and press "Control+Enter", the output is:

C:\Users\user\Desktop\Anaconda\envs\venv\python.exe
C:\Users\user\Desktop\Anaconda\envs\venv\python38.zip
attempted relative import with no known parent package
No module named 'source_code'

7. Then click on the run button at the top, the output is:

C:\Users\user\Desktop\Anaconda\envs\venv\python.exe
C:\Users\user\Desktop\Anaconda\envs\venv\python38.zip
attempted relative import with no known parent package
source_code imported

8. Then clicking back into the editor and pressing "Control+Enter" again gives:

C:\Users\user\Desktop\Anaconda\envs\venv\python.exe
C:\Users\user\Desktop\Anaconda\envs\venv\python38.zip
attempted relative import with no known parent package

I have tried including "a=8" in the "source_code/init.py" file and using "from .source_code import a" instead of "from . import source_code".

I have also tried including the lines:

from pathlib import Path as path

sys.path.insert(0, path(__file__).parent)

This changed the output from print(sys.path[0]), but made no difference to the output of the import statements.

I would like to understand the following:

1: Why does

Cannot import name "source_code" from "__main__." 

change to

"attempted relative import with no known parent package." 

when I move from outside to inside the virtual environment?

2: Why does running the script from Powershell, add the location of the file to the beginning of sys.path, but running it from spyder does not? (see the difference in line 2 between outputs 1 and 2 vs outputs 3 onwards.)

3: In Spyder, what is the difference between clicking into the editor and pressing "Control + Enter" and clicking the Run button.

4: Why can't spyder find the "source_code" module (located in the same directory as the script) when I press "Control + Enter" but it can once I have run it by clicking the run button? (see the difference between output 3 vs output 5, and output 6 vs output 8).

5a: Why (once I have run the script by clicking the run button) does pressing "Control + Enter" stop generating an ImportError but also does not run the script (i.e. it doesn't print "source_code imported" in output 5 and 8).

5b: Why does this behaviour change depending on whether I'm inside or outside the virtual environment. i.e. Why is line 3 different in outputs 4 and 5, but the same in outputs 7 and 8?

6: How do I get my script to consistently, successfully import the "source_code" module, regardless of where I run it from?