Give better errors for OS commands, like 'pip', in REPL, script

[ncoghlan]

BPO	28140
Nosy	@terryjreedy, @ncoghlan, @aroberge, @stevendaprano, @1st1, @tomviner, @pablogsal, @iritkatriel, @AlexWaygood
PRs	gh-72327: Add help message for pip in REPL #8536

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-09-14.04:40:03.485>
labels = ['interpreter-core', 'type-feature', '3.11']
title = "Give better errors for OS commands, like 'pip', in REPL, script"
updated_at = <Date 2021-11-28.19:44:25.495>
user = 'https://github.com/ncoghlan'

bugs.python.org fields:

activity = <Date 2021-11-28.19:44:25.495>
actor = 'tomviner'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2016-09-14.04:40:03.485>
creator = 'ncoghlan'
dependencies = []
files = []
hgrepos = []
issue_num = 28140
keywords = ['patch']
message_count = 8.0
messages = ['276373', '276506', '276510', '322565', '407201', '407202', '407213', '407226']
nosy_count = 9.0
nosy_names = ['terry.reedy', 'ncoghlan', 'aroberge', 'steven.daprano', 'yselivanov', 'tomviner', 'pablogsal', 'iritkatriel', 'AlexWaygood']
pr_nums = ['8536']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue28140'
versions = ['Python 3.11']

Linked PRs

• gh-72327: Suggest using system terminal for pip install in PyREPL #136328

[ncoghlan]

A problem we're starting to see on distutils-sig is folks trying to type pip commands into the Python REPL rather than their system shell, and getting cryptic syntax errors back:

>>> pip install requests
  File "<stdin>", line 1
    pip install requests
              ^
SyntaxError: invalid syntax
>>> python -m pip install requests
  File "<stdin>", line 1
    python -m pip install requests
                ^
SyntaxError: invalid syntax

This may be amenable to a similar solution to the one we used to give a custom error message for "print ":

>>> print foo
  File "<stdin>", line 1
    print foo
            ^
SyntaxError: Missing parentheses in call to 'print'

That code currently checks for "print " and "exec ", so it would be a matter of adding another special case that looked for "pip install " appearing anywhere in the string that's failing to compile (it can't be limited to the start as it may be an attempt to invoke pip via "-m")

[ncoghlan]

Paul Moore pointed out on distutils-sig that since this is mainly desired for the REPL, we can put the logic in the default excepthook rather than into the SyntaxError constructor the way we had to for "print" and "exec":

    def excepthook(typ, value, traceback):
        if typ is SyntaxError and "pip install" in value.text:
            print("'pip install' found in supplied text")
            print("Try running this from a system command prompt")
            return
        sys.__excepthook__(typ, value, traceback)

[ncoghlan]

Given that this can be done with just an excepthook change, I'm going to suggest we make the change for 3.5 and 2.7 as well.

[tomviner]

I am looking at this, as part of the EuroPython 2018 sprint.

[iritkatriel]

On 3.11:

>>> pip install requests
  File "<stdin>", line 1
    pip install requests
    ^^^^^^^^^^^
SyntaxError: invalid syntax. Perhaps you forgot a comma?

[AlexWaygood]

Similar discussion in a newer issue: https://bugs.python.org/issue45721

[terryjreedy]

I closed bpo-45721, which has additional comments, as a duplicate of this.

'print foo' now results in "SyntaxError: Missing parentheses in call to 'print'. Did you mean print(...)?"

[tomviner]

I've updated my pull request from 3 years ago. Fixed merge conflicts and addressed all comments.

#8536