The new REPL has a similar special case for when await is used at the top-level:

Maybe this could be done in a similar way?

Something like this might work:

:...skipping...
diff --git a/Lib/_pyrepl/console.py b/Lib/_pyrepl/console.py
index 8956fb1242e..833e79ef3c2 100644
--- a/Lib/_pyrepl/console.py
+++ b/Lib/_pyrepl/console.py
@@ -195,7 +195,15 @@ def runsource(self, source, filename="<input>", symbol="single"):
                 ast.PyCF_ONLY_AST,
                 incomplete_input=False,
             )
-        except (SyntaxError, OverflowError, ValueError):
+        except SyntaxError as e:
+            if "pip install" in source:  # maybe use a more general regex?
+                e.add_note(
+                    "Did you mean to run the 'pip' command?."
+                    " If so, <insert tip message here>"
+                )
+            self.showsyntaxerror(filename, source=source)
+            return False
+        except (OverflowError, ValueError):
             self.showsyntaxerror(filename, source=source)
             return False
         if tree.body:

I teach Python at the university level, and this is a pretty common issue, so I think this would be a good addition! Maybe checking if "pip install" shows up anywhere in the source string is too general, though? That would fire on input like print('pip install"), which I'm not sure is helpful.

I feel like this might want to be a more specific check, like matching the source string against something like ^\s*(py(thon3?)? -m pip|pip3?) install. I suppose you could even check for a variant involving sys.executable, though that's probably overkill (since the likely culprit here is copy/pasting general instructions from somewhere).

Ah crap, I forgot that force-pushing is frown upon here. Sorry about that!

@brianschubert thanks for the suggestion. Implementing this via the new REPL is much cleaner! I've updated my patch to use your approach.

It may be nice to include "or pip3" depending on which version they want to use.

I really don't want to get into the weeds of how to invoke pip (because the answer is "it depends" and I don't want to make this more complicated). The point of saying "try the 'pip' command" is that it can't simply be copied. The onus is on the user to invoke pip appropriately for their system. In most cases, I expect them to re-copy and paste what they just pasted/typed in.

Do we also maybe want to check for variants that start try to use sudo? So, like ^\s*(sudo )?(pip3?|py(thon3?)? -m pip) install.*?

I've never encountered someone doing that. Have your students done that before? @adqm

I'm not sure how common it is anymore, but I feel like it used to be fairly normal to suggest using sudo pip install to install things to your system's Python installation, so I wouldn't be surprised if the version with sudo was something that might still get copy/pasted in. I don't feel too strongly about this, though, just a thought.

Separately, I do agree that @ncoghlan's rephrasing of the regex is an improvement.

For the sudo question, I'd like to wait and see if we can get a sense of how this initial custom error plays out.

The sudo case is a much harder situation to provide a good error message for, as typing the sudo version into the REPL instead of the terminal can actually save people from making a system killing mistake, so we don't want to encourage them to try that specific command in the terminal.

Thanks for the review @ncoghlan!

Thanks for updating the PR to the new REPL! The previous PR stalled, I think mostly because the potential consequence of changing the site.enablerlcompleter API weren't clear, so being able to avoid that concern this time around made a big difference.