[英]Fibonacci series by recursive function in Python
Hello I am trying to generate Fibonacci series by using a recursive function in python.您好,我正在尝试通过在 python 中使用递归函数来生成斐波那契数列。
Here is my code这是我的代码
def fibolist(n):
list1 = [1, 1]
if n in (1,2) :
return list1
else:
fibolist(n-1).append(sum(fibolist(n-1)[n-3:]))
return list1
but when I enter any number as an argument, the result is [1, 1]
Could you please help me?!但是当我输入任何数字作为参数时,结果是[1, 1]
你能帮我吗?!
You start with你开始
list1 = [1, 1]
You never change that value, and then you return it to the calling routine.您永远不会更改该值,然后将其返回到调用例程。
Each invocation of fibolist
has a local variable named list1
; fibolist
每次调用都有一个名为list1
的局部变量; appending to one does not change the list1
value in the calling program.追加到一个不改变list1
中调用程序价值。 You need to explicitly do that.你需要明确地这样做。 Try尝试
else:
return fibolist(n-1) + [sum(fibolist(n-1)[n-3:])]
Just to fix your code:只是为了修复您的代码:
def fibolist(n):
if n in (0,1) :
return [1,1]
else:
return fibolist(n-1)+[sum(fibolist(n-1)[n-2:])]
Few notes:几点注意事项:
lists in python have starting index=0, so it's better start with it (unless you want to put start return to [0,1,1]
for n in (1,2)
). python中的列表有起始索引= 0,所以最好从它开始(除非你想把 start return 到[0,1,1]
for n in (1,2)
)。
Also - as already mentioned you shouldn't return local variable, which you preassign in each go.另外 - 正如已经提到的,你不应该返回局部变量,你每次都预先分配。
Your code is not updating the list1 variable that it returns upon coming back from the recursion.您的代码不会更新从递归返回时返回的 list1 变量。 Doing fibolist(n-1).append(...)
updates the list returned by the next level but that is a separate list so list1
is not affected.执行fibolist(n-1).append(...)
更新下一级返回的列表,但这是一个单独的列表,因此list1
不受影响。
You could also make your function much simpler by making it pass the last two values to itself:您还可以通过将最后两个值传递给自身来使您的函数更简单:
def fibo(n,a=1,b=1): return [a] if n==1 else [a] + fibo(n-1,b,a+b)
BTW, the modern interpretation of the fibonacci sequence starts at 0,1 not 1,1 so the above signature should be def fibo(n,a=0,b=1)
.顺便说一句,斐波那契数列的现代解释从 0,1 而不是 1,1 开始,所以上面的签名应该是def fibo(n,a=0,b=1)
。
Output:输出:
print(fibo(5))
#[1, 1, 2, 3, 5]
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