how to get the line number of an error from exec or execfile in Python

Question

Let\'s say I have the following multi-line string:

cmd = \"\"\"
    a = 1 + 1
    b = [
       2 + 2,
       4 + 4,
    ]
    bork bork bork
\"\"\"


        

Answer 1

For syntax errors, the source line number is available as the lineno flag on the exception object itself, in your case stored in err. This is specific to syntax errors where the line number is an integral part of the error:

>>> cmd = """
... 1 \ +
... 2 * "
... """
>>> try:
...   exec cmd
... except SyntaxError as err:
...   print err.lineno
... 
2

If you want to also handle other errors, add a new except block except Exception, err, and use the traceback module to compute the line number for the runtime error.

import sys
import traceback

class InterpreterError(Exception): pass

def my_exec(cmd, globals=None, locals=None, description='source string'):
    try:
        exec(cmd, globals, locals)
    except SyntaxError as err:
        error_class = err.__class__.__name__
        detail = err.args[0]
        line_number = err.lineno
    except Exception as err:
        error_class = err.__class__.__name__
        detail = err.args[0]
        cl, exc, tb = sys.exc_info()
        line_number = traceback.extract_tb(tb)[-1][1]
    else:
        return
    raise InterpreterError("%s at line %d of %s: %s" % (error_class, line_number, description, detail))

Examples:

>>> my_exec("1+1")  # no exception
>>>
>>> my_exec("1+1\nbork")
...
InterpreterError: NameError at line 2 of source string: name 'bork' is not defined
>>>
>>> my_exec("1+1\nbork bork bork")
...
InterpreterError: SyntaxError at line 2 of source string: invalid syntax
>>>
>>> my_exec("1+1\n'''")
...
InterpreterError: SyntaxError at line 2 of source string: EOF while scanning triple-quoted string