为什么jupyter笔记本只打印一次cython结果？ [英] Why jupyter notebook only prints the cython result once?

问题描述

我是cython的新手（现在仅用于一点操作）。
我使用以下代码在jupyter笔记本中查看它的一般概念。

I am new to cython(only use it for doing a little hw now). I use the following code to see a general idea of it in jupyter notebook.

%load_ext Cython
%%cython
def cfunc(int n):
    cdef int a = 0
    for i in range(n):
        a += i
    return a

print(cfunc(10))

但是，它仅打印出结果45一次。当我运行打印功能时，该单元格不会显示45个人。

However, it only prints out the result 45 once. When I run the print function, the cell doesn't show 45 anyone.

代码是否有问题？我怎样才能使单元格打印出与普通python代码相同的45格？谢谢。

Is there any problems with the code? How can I make the cell prints out 45 just the same as a normal python code? Thanks.

推荐答案

运行 %% cython 时，发生了很多魔术在引擎盖下。在详细模式下调用魔术时，可以看到部分内容，即 %% cython --verbose ：

When running %%cython-magic a lot happens under the hood. One can see parts of it when calling the magic in verbose mode, i.e. %%cython --verbose:

1. 将生成一个名为 _cython_magic_b599dcf313706e8c6031a4a7058da2a2.pyx 的文件。 b599dcf313706e8c6031a4a7058da2a2 是 %% cython 单元格的sha1哈希值，例如，它需要重新加载 %% cython 单元（请参阅此 SO-post ）


2. 此文件被cythonized并构建为c扩展名为 _cython_magic_b599dcf313706e8c6031a4a7058da2a2 。


3. 此扩展名已导入-这是您的代码打印45的时刻，此模块中的所有内容都添加到了全局命名空间。

1. A file called _cython_magic_b599dcf313706e8c6031a4a7058da2a2.pyx is generated. b599dcf313706e8c6031a4a7058da2a2 is the sha1-hash of the %%cython-cell, which is needed for example to be able to reload a %%cython-cell (see this SO-post).
2. This file is cythonized and build to a c-extension called _cython_magic_b599dcf313706e8c6031a4a7058da2a2.
3. This extension gets imported - this is the moment your code prints 45, and everything from this module is added to the global namespace.

何时如果再次执行该单元，则以上内容均不会发生：给定机器可以看到的哈希值，该单元已被执行并已加载-因此无所事事。仅当单元格的内容发生更改并因此更改其哈希值时，才会使用现金，而是执行上面的3个步骤。

When you execute the cell again, nothing of the above happens: given the sha-hash the machinery can see, that this cell was already executed and loaded - so nothing to be done. Only when the content of the cell is changed and thus its hash the cash will not be used but the 3 steps above executed.

要强制执行上述步骤，请执行以下步骤必须将-force （或 -f ）选项传递给 %% cython -magic-cell，即：

To enforce that the steps above are performed one has to pass --force (or -f) options to the %%cython-magic-cell, i.e.:

%%cython --force
...

# 45 is printed

但是，因为重新构建扩展项已经很长时间了消费者可能更喜欢以下内容

However, because building extension anew is quite time consuming one would probably prefer the following

%%cython
def cfunc(int n):
  cdef int a = 0
  for i in range(n):
    a += i
  return a

# put the code of __main__ into a function
def cython_main():
   print(cfunc(10))

# execute the old main
cython_main()

，现在在新单元格中调用 cython_main（），因此它会像普通的python代码一样重新评估会。

and now calling cython_main() in a new cell, so it gets reevaluated the same way the normal python code would.

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