Got rid of the pesky “H”, and now it works perfectly

Glad it works for you now.

I tried to submit a comment to the posted blog entry, but it rejected my first two attempts as spam, and claimed to accept my third, though it hasn’t shown up yet.

my inexperience with coding is leaking through

Coding doesn’t have anything to do with it. It is a lack of attention to detail (in other words, spelling things correctly).

It would appear that my inexperience with coding is leaking through! Got rid of the pesky “H”, and now it works perfectly. Thank you so much for your help!

Instead, the IDLE window looked like this.

And if you look on the title bar of the IDLE window, you can see that it was trying to open $(FULL_CURRENTH_PATH), not $(FULL_CURRENT_PATH); since the extra H makes it a different (undefined) variable, Notepad++ didn’t translate it into the value of the actual $(FULL_CURRENT_PATH) variable.

You mentioned:

Python … “ShellExecute - ERROR”

Sounds like you’re following the same instructions as another user did last week: asked here. We started giving advice, but the user dropped out of the conversation. Hopefully, you’ll be able to stick around long enough to get your problem solved, rather than dropping out midway through. Feel free to read through that advice first; it will help you understand where I am coming from.

I do appreciate the link to the instructions you were following. I see two three issues with their advice:

1. They want you to specify a .py as the “executable” file. That’s relying on the Windows .py association, and is where the “shell execute” message is coming from. (That helps explain things, which the other poster had neglected to inform us about.) Some run commands will work through their associations, but everything has to be set up “just so”. I would actually recommend being more explicit, rather than relying on the default association, especially since it’s giving you trouble as-is. More on this below.
2. Their python3 example command-line had spaces in the path to the “executable” (really, to the idle.py wrapper script), and following their directions for the python2 might also end up with spaces, depending on where your python2 installation really was.) Any time a path does have (or may have) a space, you should really enclose it in quotes.
3. they show smartquotes rather than real quotes; if you copy/pasted those, that’s a likely culprit.

With that said, assume for the moment (python2 or python3) that your python executable is at "c:\path to\python#\python#.exe" and that your idle.py is at "c:\path to\python#\Lib\idlelib\idle.py".
If you want to follow their advice, and rely on the Windows .py association (and assuming that the association properly handles spaces in the python path; presumably it does if you’re able to run IDLE normally), then I would suggest:

"c:\path to\python#\Lib\idlelib\idle.py" "$(FULL_CURRENT_PATH)"

(note the real quotes; note that there are quotes around each path, because there are or may be spaces)

If you want to get rid of the shell-execute interface (get rid of relying on the .py association),

"c:\path to\python#\python#.exe" "c:\path to\python#\Lib\idlelib\idle.py" "$(FULL_CURRENT_PATH)"

(I am not a command-line python expert, and the system that I’m on right now doesn’t have a python executable, so I’m not sure if python correctly cascades the remaining command-line arguments to your script. I know that perl.exe something.pl third.pl will send third.pl as the argument to the something.pl script in the perl world… I would assume python.exe behaves similarly, so that FULL_CURRENT_PATH will be sent to the idle.py script.)

If those don’t work, please let us know exactly what paths you wrote. (to avoid problems with smartquotes, surround any inline text with backticks (example: `surrounded by backticks` will render as surrounded by backticks), and use

```
big long
text
```

for inserting multiline blocks of code