Concise exception handling in Python

Question

I like to avoid the "look before you leap" paradigm because I value easy-to-read code. In some cases, I cannot predict whether an error will occur, such as resource availability or out-of-memory errors. I haven't found a clean way of writing code that is repetitious or lengthy to handle these scenarios.

The following example is marginally readable, but duplicate code is unacceptable.

try:
    myobject.write(filename)
except OSError:
    if prompt("%s is in use by another application." +
              "Close that application and try again.") == "Try again":
        myobject.write(filename) #repeated code

In order to remove the duplicate code, I must add a few more lines and indent everything, reducing the readability.

success = False
while not success:
    try:
        myobject.write(filename)
        success = True
    except OSError:
        if prompt("%s is in use by another application." +
                  "Close that application and try again.") != "Try again":
            break

Is there a shorter way of writing this in Python that doesn't duplicate code?

Answer 1

Aside from switching to while True, you could add a retry decorator, and move your retry-able code to a function decorated by retry:

from functools import wraps
from functools import update_wrapper


def retry(prompt_text="An error occured! Retry (y/n)?", 
          prompt_match='y',
          exception=Exception):
    def decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            while True:
                try:
                    ret = func(*args, **kwargs)
                    break
                except exception:
                    if raw_input(prompt_text) == prompt_match:
                        ret = None
                        break
            return ret 
        return update_wrapper(wrapper, func)
    return decorator

@retry(prompt_text="your prompt: ", prompt_match="quit", exception=OSError)
def do_write(myobject, filename):
    myobject.write(filename)

if __name__ == "__main__":
    myobject = ...
    filename = ...
    do_write(myobject, filename) # This will be retried.

It's probably only worth the effort if you're using this pattern in more than one place, though.