魔术功能时间

Question

I'm using the magic %%timeit function to get the time it takes to execute some code. The thing that bothers me is that when I run %%timeit, I don't get the results. For instace:

a=5
b=3

%%timeit
c = a + b

Now if I want to use c in the next cell, I get that c hasn't been defined.

print(c)
>>>NameError: name 'c' is not defined

Could you help me understand why this happens, why doesn't c get stored when the magic %%timeit function is used in that particular cell?

Answer 1

当您使用%%timeit计时代码时，您提供的代码将在单独的命名空间中执行，因此其效果对您的环境不可见。

Answer 2

cell mode:

 %%timeit [-n<N> -r<R> [-t|-c] -q -p<P> -o] setup_code code code... 

In cell mode, the statement in the first line is used as setup code (executed but not timed) and the body of the cell is timed. The cell body has access to any variables created in the setup code.

https://ipython.org/ipython-doc/3/interactive/magics.html#magic-timeit

You're executing in cell mode, and the line is just setup code ; which means it's not actually timed and its results are only accessible to the cell code following it.