On Wed, Oct 19, 2011 at 1:14 PM, Chris Rebert pyideas@rebertia.com wrote:
On Tue, Oct 18, 2011 at 7:14 PM, Nikolaus Rath Nikolaus@rath.org wrote:
Hello,
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()
return
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.
Cheers, Nick.
-- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia