On Sun, 22 Dec 2013 15:37:04 -0300, Frank Cui wrote:
> hey guys,
> I have a requirement where I need to sequentially execute a bunch of
> executions, each execution has a return code. the followed executions
> should only be executed if the return code is 0. is there a cleaner or
> more pythonic way to do this other than the following ?
> if a() == 0:
> if b() == 0:
> c()
I don't believe there is a clean way to deal with error return codes in
*any* language, but certainly not Python.
If you only have a few such functions, you can mis-use boolean operators
to get the result you want, at the cost of misleading code:
a() == 0 and b() == 0 and c()
But that's pretty horrible code, because it looks like you're testing a
condition when you're really trying to run a, b, c etc. for their side-
effects. Code that relies on side-effects is usually a sign of poor
design.
A better alternative is to modify the functions so that instead of
returning 0 on failure and (I'm guessing here) None on success, they
raise an exception instead. Instead of:
def a():
do_this()
do_that()
if condition:
return 0
do_something_else()
you re-write it as:
def a():
do_this()
do_that()
if condition:
raise SomeError("something broke")
do_something_else()
Then you can do this:
try:
a()
b()
c()
except SomeError:
handle_error()
What if you can't edit all the various a, b, c functions because other
parts of your code rely on them returning an error result? That's easy,
you just need an adaptor:
import functools
def adapt(func):
@functools.wraps(func)
def inner(*args, **kwargs):
result = func(*args, **kwargs)
if result == 0:
raise SomeError("some message")
return inner
try:
adapt(a)()
adapt(b)()
adapt(c)()
except SomeError:
handle_error()
Another option really only applies if all the functions use the same set
of arguments.
def chain(list_of_functions, *args, **kwargs):
for func in list_of_functions:
result = func(*args, **kwargs)
if result == 0:
break
--
Steven
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