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

Dietrich Bollmann diresu at web.de
Tue Apr 22 17:12:47 CEST 2008


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







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