On Tue, Mar 25, 2014 at 10:44 AM, Mark H Harris <harrismh...@gmail.com> wrote:
> On 3/24/14 6:01 PM, Chris Angelico wrote:
>
>> Easy fix. Use the "explicit capture" notation:
>> adders[n] = lambda a, n=n: a+n
>> And there you are, out of your difficulty at once!
> But, and this is the big (WHY?) is that necessary? In other words, its
> not about experts knowing how to make this work, its about "normal" people
> not understanding in the first place why its a problem, and why the various
> solutions work to fix it; even though "we" all know that nothing is
> 'broken'.
Why is it necessary? For the same reason that this works:
def func_pair():
x = 0
def inc():
nonlocal x; x+=1
return x
def dec():
nonlocal x; x-=1
return x
return inc, dec
fooup, foodn = func_pair()
barup, bardn = func_pair()
>>> fooup(), fooup(), fooup(), foodn()
(1, 2, 3, 2)
>>> barup(), barup(), bardn(), bardn()
(1, 2, 1, 0)
When you use the variable x in multiple places, it's the same variable
and it has a single value. If you don't want that, you have to make a
separate variable.
ChrisA
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