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From: Gabriel Genellina on 7 Apr 2010 23:52
En Wed, 07 Apr 2010 17:23:22 -0300, kwatch <kwatch(a)gmail.com> escribi�:

> 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

From: kwatch on 9 Apr 2010 22:19
On 4月8日, 午後12:52, "Gabriel Genellina" <gagsl-...(a)yahoo.com.ar> wrote:
>
> 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

Thank you Gabriel,
this is great help for me.

By the way, is it hard to specify any other exception class instead of
SyntaxError?
The SyntaxError class is a good solution in my case, but if possible,
I want to know
more general solution to specify filename and linenum for exception.

--
makoto
From: Gabriel Genellina on 12 Apr 2010 14:23
En Fri, 09 Apr 2010 23:19:48 -0300, kwatch <kwatch(a)gmail.com> escribió:

> On 4月8日, 午後12:52, "Gabriel Genellina" <gagsl-...(a)yahoo.com.ar> wrote:
>>
>> 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
>>
>
> By the way, is it hard to specify any other exception class instead of
> SyntaxError?
> The SyntaxError class is a good solution in my case, but if possible,
> I want to know
> more general solution to specify filename and linenum for exception.

You can always store any info you want in the exception object, just write
__str__ accordingly.
The advantage of SyntaxError is that it is special-cased in the
interpreter itself as to add some spaces and the ^ character.
The disadvantages are already pointed out by Dennis Lee Bieber and aren't
minor.

--
Gabriel Genellina

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