为什么numpy的array那么快？-Python教程-PHP中文网

为什么numpy的array那么快？

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发布： 2016-06-06 16:24:28

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在python numpy中，如果我用10^6长度随机生成的list生成numpy array,那么生成耗时0.1s, 但是得到这个array的mean只需要init的2%的时间。而我自己implement的array得到mean需要十几秒。
所以numpy的array十分黑科技是应为:
1)用底层代码太厉害？
2)init的时候partially compute了某一些中间量？(应为求mean的时间比access慢，比O(n)快 )
如果是2的话能否讲一下大概思路(不需要用python O(n)就能得mean)？
感激不禁！

回复内容：

numpy的许多函数不仅是用C实现了，还使用了BLAS（一般Windows下link到MKL的，Linux下link到OpenBLAS）。基本上那些BLAS实现在每种操作上都进行了高度优化，例如使用AVX向量指令集，甚至能比你自己用C实现快上许多，更不要说和用Python实现的比。。你用blas试试 numpy底层使用BLAS做向量，矩阵运算。像求平均值这种vector operation，很容易使用multi-threading或者vectorization来加速。比如MKL就有很多优化。

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