How to repeat something upon exception in python?

Question

What is the most elegant way to repeat something after it caused an exception in python?

I have something like this [pseudo code as an example]:

try:
  do_some_database_stuff()
except DatabaseTimeoutException:
  reconnect_to_database()
  do_some_database_stuff() # just do it again

But imagine if I don't have a nice function but a lot of code instead. Duplicate code is not very nice.

So I think this is slightly better:

while True:
  try:
    do_some_database_stuff()
    break
  except DatabaseTimeoutException:
    reconnect_to_database()

That's good enough if the exception really fixes the problem. If not I need a counter to prevent an indefinite loop:

i = 0
while i < 5:
  try:
    do_some_database_stuff()
    break
  except DatabaseTimeoutException:
    reconnect_to_database()
    i += 1

But then I don't really know if it worked so it's also:

while i <= 5:
  try:
    do_some_database_stuff()
    break
  except DatabaseTimeoutException:
    if i != 5:
     reconnect_to_database()
    else:
      raise DatabaseTimeoutException
    i += 1

As you can see it starts to get very messy.

What is the most elegant way of expressing this logic?

• try something
• if it fails apply fix
• try n more times including the fix
• if it continues to fail give me an error to prevent a indefinite loop

Answer 1

You can use a "for-else" loop:

for ii in range(5):
    try:
        do_some_database_stuff()
        break
    except DatabaseTimeoutException:
        reconnect_to_database()
else:
    raise DatabaseTimeoutException

Or, without:

for ii in range(5):
    try:
        do_some_database_stuff()
        break
    except DatabaseTimeoutException:
        if ii == 4:
            raise
        reconnect_to_database()