Repeat Python function call on exception?

Question

Hey everybody I\'m working on a data scraping project and I\'m looking for a clean way to repeat a function call if an exception is raised.

Pseudo-code:

Answer 1

To do precisely what you want, you could do something like the following:

import functools
def try_x_times(x, exceptions_to_catch, exception_to_raise, fn):
    @functools.wraps(fn) #keeps name and docstring of old function
    def new_fn(*args, **kwargs):
        for i in xrange(x):
            try:
                return fn(*args, **kwargs)
            except exceptions_to_catch:
                 pass
        raise exception_to_raise
    return new_fn

Then you just wrap the old function in this new function:

#instead of
#risky_method(1,2,'x')
not_so_risky_method = try_x_times(3, (MyError,), myError2, risky_method)
not_so_risky_method(1,2,'x')

#or just
try_x_times(3, (MyError,), myError2, risky_method)(1,2,'x')

Answer 2

Use a loop

i = 0
while True:
  try: myfunc(x); break;
  except myError:
    i = i + 1;
    # print "Trying again"
    if i > 5: raise myError2;

Answer 3

success = False
attempts = 0
while not success and attempts < 10: # or however many times you want to attempt
    try:
        functionCall()
        success = True
    except:
        i += 1
if not success:
    raise functionCallFailedError

Hope this helps

Answer 4

To raise Exception as usual after n retries

from functools import wraps

def retry(times):
    """
    Decorator to retry any functions 'times' times.
    """
    def retry_decorator(func):
        @wraps(func)
        def retried_function(*args, **kwargs):
            for i in range(times - 1):
                try:
                    func(*args, **kwargs)
                    return
                except Exception:  
                    pass
            func(*args, **kwargs)

        return retried_function

    return retry_decorator


# test

attempts = 3

@retry(4)
def function_that_raises_error():
    global attempts
    if 0 < attempts:
        print("fail")
        attempts -= 1
        raise Exception

    print("pass")

function_that_raises_error()

Answer 5

I like to do these problems with recursion:

def tryfor(times, on_failure, excepts, func, *args, **kwargs):
    if times < 1:
        raise on_failure()
    try:
        return func(*args, **kwargs)
    except excepts:
        return tryfor(times-1, on_failure, excepts, func, *args, **kwargs)


tryfor(3, PermanentException, (SomeError,), dostuff,1,2)

Answer 6

for x in xrange(num_retries):
    try:
        myFunc()
    except MyError, err:
        continue
        #time.sleep(1)
    err = None
    break
if err:
    raise MyError2
#else:
#    print "Success!"