Error in Extending/Embedding FAQ, point 16: How do I tell "incomplete input" from "invalid input"?

[Dietrich Bollmann]

Hi,

I found a solution thanks to another posting on c++-sig and an answer by
Andreas Klöckner :)

Thank you, Andreas!

The thread is here: 
  http://mail.python.org/pipermail/c++-sig/2008-April/thread.html#13470

I would like to inform the responsible of the Python Extending/Embedding
FAQ, http://www.python.org/doc/faq/extending/ about the broken code in
the FAQ and the solution I found.

I hope this might prevent other people from the frustration I found
myself in this morning  (...but unfortunately also, at least partly,
from the joy I am experiencing now, after finding the new solution :).

Does anybody know how to contact the person in charge?

Thanks, 

Dietrich

PS:

Of course, I still wonder about the "invalid syntax" error message /
code I wrote about. But ok, I hope there will be some more adequate
error message / code some day in the future :)

On Wed, 2008-04-23 at 01:09 +0900, Dietrich Bollmann wrote:
> On Wed, 2008-04-23 at 00:12 +0900, Dietrich Bollmann wrote:
> > The following code for example:
> > 
> >   >>> eins = [1,
> >   ...     2,
> >   ...     3]
> >   >>> 
> > 
> > is accepted without any problem by the Python shell.
> > 
> > When using the code from the FAQ and entering it line by line 
> > already the second line causes a simple "invalid syntax" error:
> > 
> >   >>> eins = [1,
> >   ...     2,
> >     File "<stdin>", line 2
> >       2,
> >        ^
> >   SyntaxError: invalid syntax
> 
> By the way - isn't this error message / error code just "wrong" in
> the given situation and therefor kind of a "bug"?
> 
> An "end of file" or "incomplete input" error at least would 
> describe the situation much better - and be a better base for
> functionality which is based the error code also.
> 
> ---
> 
> I also thought that I should explain a little bit more exactly, 
> what I am intending to do with the code based on 
> paragraph 16 (How do I tell "incomplete input" from "invalid input"?)
> of the Extending/Embedding FAQ:
> 
> I am using Python as scripting language in an application (blender).
> In order to interface this application from other programs
> I programmed a python command port / command socket 
> for this application.
> 
> Between other clients I also wrote a shell client which connects via 
> the command port to the application.  My goal is to make it as similar
> to a normal python shell as possible - and therefor I try to also mimic
> the "intelligent" way of the Python shell to react to Python input:
> 
>   - when entering a line which is a complete input,
>     it is immediately evaluated by the shell and the 
>     result is printed.
> 
>   - when the last entered line is erroneous, 
>     an error message is printed immediately
> 
>   - when the input is incomplete, Python waits
>     for other lines to complete the input
> 
>   - when the line is part of a function definition etc.
>     python waits until an empty line is entered
>     before accepting the input as complete.
> 
> My problem is to understand when an input is erroneous and
> when it is incomplete - which is impossible with an error message
> like "invalid syntax"...
> 
> So here again my question: How can I make the difference
> between an incomplete and an erroneous input?
> 
> The code examples in the FAQ worked fine until now - but do not
> anymore for the current Python implementation.
> 
> Thanks, Dietrich
> 
> By the way:  Does anybody know who is responsible for the FAQ
> and could adapt the examples to the current Python version
> by changing the code / annotating it? 
> 
> 
> On Wed, 2008-04-23 at 00:12 +0900, Dietrich Bollmann wrote:
> Hi, 
> > 
> > Both code examples from paragraph 16 from the Python Extending /
> > Embedding FAQ - 'How do I tell "incomplete input" from "invalid
> input"?'
> > -
> >
> ( http://www.python.org/doc/faq/extending/#how-do-i-tell-incomplete-input-from-invalid-input ) do not work with the current state of Python anymore.
> > 
> > In the second code example, the error message returned by Python is
> > checked in order to differentiate errors caused by an incomplete input
> > from other syntax errors:
> > 
> >    if (PyArg_ParseTuple (val, "sO", &msg, &obj) &&
> >             !strcmp (msg, "unexpected EOF while parsing")) /* E_EOF */
> > 
> > In the current Python version there are more error messages indicating
> an 
> > incomplete Python input and I could make the code work for a while 
> > by adding the following strings to the condition:
> > 
> > 		/* error messages indicating an incomplete input */
> > 		if (PyArg_ParseTuple(error, "sO", &message, &obj) &&
> > 			(!strcmp(message, "unexpected EOF while parsing") ||
> > 			 !strcmp(message, "expected an indented block")   ||
> > 			 !strcmp(message, "EOF while scanning triple-quoted string")
> > 			 )
> > 			) { /* E_EOF */
> > 
> > but recently there are also cases which generate error messages
> > which are too general to be added to this list.
> > 
> > The following code for example:
> > 
> >   >>> eins = [1,
> >   ...     2,
> >   ...     3]
> >   >>> 
> > 
> > is accepted without any problem by the Python shell.
> > 
> > When using the code from the FAQ and entering it line by line 
> > already the second line causes a simple "invalid syntax" error:
> > 
> >   >>> eins = [1,
> >   ...     2,
> >     File "<stdin>", line 2
> >       2,
> >        ^
> >   SyntaxError: invalid syntax
> > 
> > which is to general to be integrated into the list of tested 
> > error messages as it might be caused also by code like:
> > 
> >   >>> one two
> >     File "<stdin>", line 1
> >       one two
> >             ^
> >   SyntaxError: invalid syntax
> > 
> > which generates an "invalid syntax" error even in the Python shell.
> > 
> > I also tried the first code example of paragraph 
> > '16   How do I tell "incomplete input" from "invalid input"?'
> > of the FAQ in order to see if it could be used to make the 
> > difference between syntax errors and incomplete code errors.  
> > But - as in the case before - the returned error
> > code is E_SYNTAX (14 = Syntax error) and not E_EOF (11 = End Of File)
> > as should be expected.
> > 
> > Is there anybody who has an idea how to differentiate the 
> > first case from the second in order to mimic the behaviour of 
> > the Python shell from c code?  
> > 
> > If this shouldn't be possible lists split into different lines
> > couldn't be accepted anymore or the feature of the Python shell 
> > to described in paragraph 16 of the faq:
> > 
> >   Sometimes you want to emulate the Python interactive interpreter's 
> >   behavior, where it gives you a continuation prompt when the input 
> >   is incomplete (e.g. you typed the start of an "if" statement or you 
> >   didn't close your parentheses or triple string quotes), but it
> gives 
> >   you a syntax error message immediately when the input is invalid.
> > 
> > would have to be given up and every entered line of code would have
> to 
> > be terminated by an empty line before evaluation :(
> > 
> > Thanks for any help, Dietrich
> > 
> > 
> > 
> > 
> 
>