Steve Holden wrote:
> Gigs_ wrote:
>> sorry i think that i express wrong. having problem with english
>>
>>
>> what i mean is how python knows to add all thing at the end of recursion
>>
>> >>> def f(l):
>> if l == []:
>> return []
>> else:
>> return f(l[1:]) + l[:1]
>>
>>
>> f([1,2,3])
>>
>> recursion1 f([2,3]) + [1]
>>
>> recursion2 f([3]) + [2] or [2, 1]?
>>
>> recursion3 f([]) + [3] or [3, 2, 1]
>>
>>
>> i dont get all this
>>
>> >>> def f(l):
>> if l == []:
>> print l
>> return []
>> else:
>> return f(l[1:]) + l[:1]
>>
>> >>> f([1,2,3])
>> []
>> [3, 2, 1] # how this come here? how python save variables from each
>> recursion?
>>
>>
>> sorry again for first post
>>
> I think the thing you are missing is that the recursive call f(l[1:]) in
> the return statement causes the current call to be suspended until the
> recursive call is complete. The new call has its own value for l, which
> is the caller's l[1:]. Each new call creates a completely new namespace.
>
> A less complicated function might make it a little more obvious.
>
> def factorial(n):
> print "n =", n
> if n=0:
> return 1
> else:
> return n * factorial(n-1)
>
> Try running that with a few different arguments to show you how the
> recursion works.
>
> regards
> Steve
>>> def factorial(n):
print "n =", n
if n==0:
return 1
else:
return n * factorial(n-1)
>>> factorial(3)
n = 3
n = 2
n = 1
n = 0
6
now i understand. but one question at the end this function return 1. how
python
knows that it needs to multiply 1 with all recursive returns. (why python didnt
sum recursive return with 1?)
that will be all, thanks in advance
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