Russell Brennan wrote:
> I'm going to x-post this to stackoverflow but...
>
> When checking a method's arguments to see whether they were set, is it
> pythonic to do an identity check:
>
> def doThis(arg1, arg2=None):
> if arg2 is None:
> arg2 = myClass()
>
>
> Or is it proper form to use a short-circuiting boolean:
>
> def doThis(arg1, arg2=None):
> arg2 = arg2 or myClass()
When I read this I always have to stop and consider whether there are valid
falsey arguments that could be passed as arg2.
An obvious example is
def do_this(arg=None):
arg = arg or []
arg.append(42)
a = []
do_this(a)
do_this(a)
print(a) # expected: [42, 42] actual output: []
Choosing the first approach is not just a matter of style, it avoids a
source of subtle bugs.
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