CODEWITHSUNDEEP
pythonpython-2.7decoratorpython-decorators
RoyHB
RoyHB

Reputation: 1725

wrapping class method in try / except using decorator

I have a general purpose function that sends info about exceptions to an application log. I use the exception_handler function from within methods in classes. The app log handler that is passed into and called by the exception_handler creates a JSON string that is what actually gets sent to the logfile. This all works fine.

def exception_handler(log, terminate=False):
    exc_type, exc_value, exc_tb = sys.exc_info()
    filename, line_num, func_name, text = traceback.extract_tb(exc_tb)[-1]
    log.error('{0} Thrown from module: {1} in {2} at line: {3} ({4})'.format(exc_value, filename, func_name, line_num, text))
    del (filename, line_num, func_name, text)
    if terminate:
        sys.exit()

I use it as follows: (a hyper-simplified example)

from utils import exception_handler

class Demo1(object):
    def __init__(self):
        self.log = {a class that implements the application log}

    def demo(self, name):
        try:
            print(name)
        except Exception:
            exception_handler(self.log, True)

I would like to alter exception_handler for use as a decorator for a large number of methods, i.e.:

@handle_exceptions
def func1(self, name)
    {some code that gets wrapped in a try / except by the decorator}

I've looked at a number of articles about decorators, but I haven't yet figured out how to implement what I want to do. I need to pass a reference to the active log object and also pass 0 or more arguments to the wrapped function. I'd be happy to convert exception_handler to a method in a class if that makes things easier.

Upvotes: 8

Views: 7770

Answers (2)

Martijn Pieters
Martijn Pieters

Reputation: 1122182

Such a decorator would simply be:

def handle_exceptions(f):
    def wrapper(*args, **kw):
        try:
            return f(*args, **kw)
        except Exception:
            self = args[0]
            exception_handler(self.log, True)
    return wrapper

This decorator simply calls the wrapped function inside a try suite.

This can be applied to methods only, as it assumes the first argument is self.

Upvotes: 16

RoyHB
RoyHB

Reputation: 1725

Thanks to Martijn for pointing me in the right direction. I couldn't get his suggested solution to work but after a little more searching based on his example the following works fine:

def handle_exceptions(fn):
    from functools import wraps
    @wraps(fn)
    def wrapper(self, *args, **kw):
        try:
            return fn(self, *args, **kw)
        except Exception:
            exception_handler(self.log)
    return wrapper

Upvotes: 4

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