[Q] raise exception with fake filename and linenumber

[Gabriel Genellina]

En Wed, 07 Apr 2010 17:23:22 -0300, kwatch <kwatch at gmail.com> escribió:

> Is it possible to raise exception with custom traceback to specify
> file and line?
> I'm creating a certain parser.
> I want to report syntax error with the same format as other exception.
> -------------------------
> 1: def parse(filename):
> 2:     if something_is_wrong():
> 3:         linenum = 123
> 4:         raise Exception("syntax error on %s, line %s" % (filename,
> linenum))
> 5:
> 6: parse('example.file')
> -------------------------
>
> my hope is:
> -------------------------
> Traceback (most recent call last):
>   File "/tmp/parser.py", line 6, in <module>
>     parse('example.file')
>   File "/tmp/parser.py", line 4, in parse
>     raise Exception("syntax error on %s, line %s" % (filename,
> linenum))
>   File "/tmp/example.file", line 123
>     foreach item in items   # wrong syntax line
> Exception: syntax error
> -------------------------

The built-in SyntaxError exception does what you want. Constructor  
parameters are undocumented, but they're as follows:

    raise SyntaxError("A descriptive error message", (filename, linenum,  
colnum, source_line))

colnum is used to place the ^ symbol (10 in this fake example). Output:

Traceback (most recent call last):
   File "1.py", line 9, in <module>
     foo()
   File "1.py", line 7, in foo
     raise SyntaxError("A descriptive error message", (filename, linenum,  
colnum, "this is line 123 in example.file"))
   File "example.file", line 123
     this is line 123 in example.file
              ^
SyntaxError: A descriptive error message

-- 
Gabriel Genellina