[Python-ideas] Reporting unmatched parentheses in SyntaxError messages?

[Andrew Barnert]

On Jul 7, 2015, at 22:53, Nick Coghlan <ncoghlan at gmail.com> wrote:
> 
> One of the more opaque error messages new Python users can encounter
> is a syntax error due to unmatched parentheses:
> 
>    File "/home/me/myfile.py", line 11
>        data = func()
>        ^
>    SyntaxError: invalid syntax
> 
> While I have no idea how we could implement it, I'm wondering if that
> might be clearer if the error message instead looked more like this:
> 
>    File "/home/me/myfile.py", line 11
>        data = func()
>        ^
>    SyntaxError: invalid syntax (Unmatched '(' on line 10)
> 
> Or, similarly,
> 
>    SyntaxError: invalid syntax (Unmatched '[' on line 10)
>    SyntaxError: invalid syntax (Unmatched '{' on line 10)
> 
> I'm not sure it would be feasible though - we generate syntax errors
> from a range of locations where we don't have access to the original
> token data any more :(

Do we know that there's an unbalanced parens (or bracket or brace) even when we don't know where it is? I think this would still be sufficient:

   File "/home/me/myfile.py", line 11
       data = func()
       ^
   SyntaxError: invalid syntax (Unmatched '(', possibly on a previous line)

Really, just telling people to look at a previous line for unmatched pairs is sufficient to solve the problem every time it comes up on #python, StackOverflow, etc.

(Of course this would take away a great opportunity to explain to novices why they might want to use a better editor than Notepad, something which can show them mismatched parens automatically.)
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