Brief exception handling in Python

Question

I like to avoid the “watch before jumping” paradigm because I value easy-to-read code. In some cases, I cannot predict whether an error will occur, such as resource availability or memory errors. I have not found a clean way to write code that is repeatable or lengthy to process these scripts.

The following example is minimally readable, but duplicate code is not acceptable.

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

To remove duplicate code, I have to add a few more lines and indents, reducing 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 to write this in Python that doesn't duplicate code?

Answer 1

while True, retry , , , 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.

, , .

Answer 2

Python, ?

. , while True: success:

while True:
    try:
        myobject.write(filename)
        break
    except OSError:
        if prompt("%s is in use by another application."
                  "Close that application and try again.") != "Try again":
            break

, , .

, , + if-statement. , .

Answer 3

, , :

class exception_handler(object):

    def __init__(self, prompt_text, prompt_match, exception):
        self.prompt = prompt_text
        self.match = prompt_match
        self.exception = exception

    def __call__(self, f):
        def wrapped_f(*args, **kwargs):
            while True:
                try:
                    f(*args, **kwargs)
                    break
                except self.exception:
                    if raw_input(self.prompt) == self.match:
                        break       
        return wrapped_f


@exception_handler("your prompt (type 'quit' to exit): ", "quit", OSError)
def f(filename):
    print("before writing to file: {}".format(filename))
    # myobject.write(filename)
    raise OSError("testing...")