On Wed, Oct 19, 2011 at 1:14 PM, Chris Rebert firstname.lastname@example.org wrote:
On Tue, Oct 18, 2011 at 7:14 PM, Nikolaus Rath Nikolaus@rath.org wrote:
I often have code of the form:
def my_fun(): allocate_res1() try: # do stuff allocate_res2() try: # do stuff allocate_res3() try: # do stuff finally: cleanup_res3() finally: cleanup_res2() finally: cleanup_res1()
With increasing number of managed resources, the indentation becomes really annoying, there is lots of line noise, and I don't like the fact that the cleanup is so far away from the allocation.
Use the `with` statement and context managers. They were added for this exact situation. See http://www.python.org/dev/peps/pep-0343/
Resulting code will resemble:
def func(): with alloc() as res1, alloc() as res2, alloc() as res3: # do stuff
Or, to more closely mirror the original example:
# Define these wherever the current resources are defined @contextlib.contextmanager def cm1(): res1 = allocate_res1() try: yield res1 finally: cleanup_res1()
@contextlib.contextmanager def cm2(): res2 = allocate_res2() try: yield res2 finally: cleanup_res2()
@contextlib.contextmanager def cm3(): res3 = allocate_res3() try: yield res2 finally: cleanup_res3()
def func(): with cm1() as res1: # do stuff with cm2() as res2: # do stuff with cm3() as res3: # do stuff
Any time a with statement's body consists solely of another with statement you can collapse them into one line as Chris did in his example.