Consider the following:
with open(path, mode) as f:
return [line for line in f if condition]
Will the file be closed properly, or does using return
somehow bypass the context manager?
Yes, it acts like the finally
block after a try
block, i.e. it always executes (unless the python process terminates in an unusual way of course).
It is also mentioned in one of the examples of PEP-343 which is the specification for the with
statement:
with locked(myLock):
# Code here executes with myLock held. The lock is
# guaranteed to be released when the block is left (even
# if via return or by an uncaught exception).
Something worth mentioning is however, that you cannot easily catch exceptions thrown by the open()
call without putting the whole with
block inside a try..except
block which is usually not what one wants.