gh-72327: Add help message for pip in REPL

[tomviner]

New users to Python sometimes type pip install commands into the REPL, not realising it won't work. This change attempts to give them guidance.

The message shown, is based on: ipython/ipython@67d1300#diff-df33ce94589aa1d71aef98241dbcd729R391

https://bugs.python.org/issue28140

• Issue: Give better errors for OS commands, like 'pip', in REPL, script #72327

[tomviner]

Thanks for the review @serhiy-storchaka. I've addressed all your points.

[ncoghlan]

Nice! This feels similar in spirit to the change we made for print statement syntax, but easier to handle at the excepthook level since we don't need to worry about the non-interactive case.

[serhiy-storchaka]

Since there is a chance of false detection, it is worth to include the original message in the result.

[tomviner]

The original message is just "invalid syntax", so to put that back in would require going from what we have now:

  File "<string>", line 1
    pip install qwerty
              ^
SyntaxError: The Python package manager (pip) can only be used from outside of Python.
Please try the `pip` command in a separate terminal or command prompt.

to something like the more expansive:

  File "<string>", line 1
    pip install qwerty
              ^
SyntaxError: invalid syntax

Note: The Python package manager (pip) can only be used from outside of Python.
Please try the `pip` command in a separate terminal or command prompt.

I'm happy with either.

[serhiy-storchaka]

It is not always "invalid syntax".

>>>     x = 'pip install'
  File "<stdin>", line 1
    x = 'pip install'
    ^
IndentationError: unexpected indent

[tomviner]

I think this is why the original suggestion from ncoghlan has is SyntaxError rather than isinstance, so subclasses (IndentationError & TabError) don't get caught.

[serhiy-storchaka]

It is not always "invalid syntax" even if the type is SyntaxError.

>>> x = ['pip install')
  File "<stdin>", line 1
    x = ['pip install')
                      ^
SyntaxError: closing parenthesis ')' does not match opening parenthesis '['

Also I think that we perhaps can use __notes__ here.

[ghost]

All commit authors signed the Contributor License Agreement.

[serhiy-storchaka]

@tomviner, please sign the CLA again for both of your email addresses by clicking the button above. It is now required sign it for register email addresses instead of b.p.o accounts.

@iritkatriel, could you please take a look? Is this a correct use of __notes__?

@ncoghlan, as the main proponent of such changes, could you please look at it again? Does the message look good to you?

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[serhiy-storchaka]

My apologies, @tomviner, but it seems that there are now conflicts with other changes made in the last 9 months. Could you please resolve them?

@ncoghlan, could you please check that this PR completely implements your request?

I did not see anything wrong, so if this is what we need, I'm going to merge this PR after resolving conflicts.

[ncoghlan]

Thanks for the ping @serhiy-storchaka, this had definitely dropped off my review radar.

I think we still want one slight API tweak, so enablerlcompleter becomes purely a legacy compatibility API for third party code to use that the interpreter itself bypasses.

[ncoghlan]

I think this change to the way enablerlcompleter works is still concerning.

Reviewing 0e6d9e2 I think the public API to preserve would be:

1. New top level function that actually does the registration is called _register_readline (as @tomviner originally had it)
2. Reduced enablerlcompleter implementation just does sys.__interactive_hook__ = _register_readline
3. _set_interactive_hook call _register_readline directly, bypassing enablerlcompleter (since it is setting its own hook)

enablerlcompleter would never be called by the standard library (outside the test suite), it would purely be a backwards compatibility API accounting for the fact that it was never marked as private in the interactive help.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.