在递归函数中将大列表作为参数传递时的性能? [英] Performance when passing huge list as argument in recursive function?

问题描述

我正在使用 Python 并且我有一个递归函数，它将一个巨大的列表作为参数之一:

I am using Python and I have a recursive function that takes a huge list as one of the arguments:

# Current implementation
def MyFunction(arg1, arg2, my_huge_list)
    ...
    ...
    MyFunction(new_arg1, new_arg2, my_huge_list)

如上所示，MyFunction 使用相同 列表my_huge_list 递归调用；与其他参数不同，这不会改变.而且，这个列表是巨大的.我的一个朋友建议我可以把 my_huge_list 当作一个全局变量来提高性能，否则这个庞大的列表可能会在每次迭代中一遍又一遍地复制.

As you can see above, MyFunction is called recursively using the same list my_huge_list; this doesn't change, unlike the other arguments. And, again, this list is huge. A friend of mine suggested that I could treat my_huge_list as a global variable to improve the performance, as otherwise this huge list may be copied over and over in every iteration.

# Friend's suggestion

MyHugeList=[a,b,c, ...and many many other elements... ]

def MyFunction(arg1, arg2)
    global MyHugeList
    ...
    ...
    MyFunction(new_arg1, new_arg2)

使用如上所示的全局变量是否比原始版本提高了算法的性能?我的程序运行了数周，所以从长远来看，即使是轻微的改进也可能是有价值的.

Does using a global variable as shown above improve the performance of the algorithm over the original version? My program runs for weeks, so even a slight improvement may be valuable in the long run.

推荐答案

列表将通过引用传递，因此不再需要传输 1 项列表与 100000 项列表:

The list will be passed by reference, so it doesn't take any longer to transfer a 1-item list vs. a 100000 item list:

def null(x): return x
longlist = range(100000)
shortlist = range(1)
longerlist = range(1000000)

%timeit null(shortlist)
10000000 loops, best of 3: 124 ns per loop

%timeit null(longlist)
10000000 loops, best of 3: 137 ns per loop

%timeit null(longerlist)
10000000 loops, best of 3: 125 ns per loop

较长的列表中有 100k 和 1M 的条目，但与较短的列表相比，作为参数传递的时间并不长.

The longer lists have 100k and 1M entries in them, and yet don't take significantly long to pass as arguments than shorter lists.

可能还有其他方法可以提高性能；这可能不是其中之一.

there may be other ways to improve performance; this probably isn't one of them.

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