Arnaud Delobelle a écrit :
> Hi all,
>
> Imagine I have three functions a(x), b(x), c(x) that each return
> something or raise an exception. Imagine I want to define a function
> that returns a(x) if possible, otherwise b(x), otherwise c(x),
> otherwise raise CantDoIt.
>
> Here are three ways I can think of doing it:
>
> ----------
> # This one looks ugly
Yes.
> def nested_first(x):
> try:
> return a(x)
> except:
<side-note>
Try avoiding bare except clauses. It's usually way better to specify the
type(s) of exception you're expecting to catch, and let other propagate.
</side-note>
> try:
> return b(x)
> except:
> try:
> return c(x)
> except:
> raise CantDoIt
>
> # This one looks long-winded
Yes. And not's very generic.
> def flat_first(x):
> try:
> return a(x)
> except:
> pass
> try:
> return b(x)
> except:
> pass
> try:
> return c(x)
> except:
> raise CantDoIt
>
> # This one only works because a,b,c are functions
It works with any callable. Anyway, what else would you use here ???
> # Moreover it seems like an abuse of a loop construct to me
Why so ? loops are made for looping, adn functions are objects like any
other.
> def rolled_first(x):
> for f in a, b, c:
> try:
> return f(x)
> except:
> continue
> raise CantDoIt
Here's an attempt at making it a bit more generic (<side-note>it still
lacks a way to specify which kind of exceptions should be silently
swallowed</side-note>.
def trythese(*functions):
def try_(*args, **kw):
for func in functions:
try:
return func(*args, **kw)
except: # FIX ME : bare except clause
pass
else:
# really can't do it, sorry
raise CantDoIt
return try_
result = trythese(a, b, c)(x)
> ----------
> # This one isn't correct but looks the clearest to me
> def wished_first(x):
> try:
> return a(x)
> except:
> return b(x)
> except:
> return c(x)
> except:
> raise CantDoIt
Having multiple except clauses is correct - but it has another semantic.
> Note: I've chosen functions a, b, c, but really I'm looking for a way
> that is suitable for any chunk of code.
A function is an object wrapping a chunk of code...
I personnaly find the loop-based approach quite clean and pythonic.
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