[Q] raise exception with fake filename and linenumber
kwatch
Is it possible to raise exception with custom traceback to specify
file and line?
Situation
=========
I'm creating a certain parser.
I want to report syntax error with the same format as other exception.
Example
=======
parser.py:
-------------------------
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')
-------------------------
current result:
-------------------------
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))
Exception: syntax error on example.file, line 123
-------------------------
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
-------------------------
I guess I must create dummy traceback data, but I don't know how to do
it.
Could you give me an advice?
Thank you.
--
regards,
makoto kuwata
Gabriel Genellina
> 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
kwatch
>
> 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
Gabriel Genellina
> On 4月8日, 午後12:52, "Gabriel Genellina" <gagsl-...@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