How to store the result from %%timeit cell magic?

Question

I can't figure out how to store the result from cell magic - %%timeit? I've read:

1. Can you capture the output of ipython's magic methods?
2. Capture the result of an IPython magic function

and in this questions answers only about line magic. In line mode (%) this works:

In[1]: res = %timeit -o np.linalg.inv(A)

But in cell mode (%%) it does not:

In[2]: res = %%timeit -o 
       A = np.mat('1 2 3; 7 4 9; 5 6 1')
       np.linalg.inv(A)

It simply executes the cell, no magic. Is it a bug or I'm doing something wrong?

Answer 1

You can use the _ variable (stores the last result) after the %%timeit -o cell and assign it to some reusable variable:

In[2]: %%timeit -o 
       A = np.mat('1 2 3; 7 4 9; 5 6 1')
       np.linalg.inv(A)
Out[2]: blabla
        <TimeitResult : 1 loop, best of 3: 588 µs per loop>

In[3]: res = _

In[4]: res
Out[4]: <TimeitResult : 1 loop, best of 3: 588 µs per loop>

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I don't think it's a bug because cell mode commands must be the first command in that cell so you can't put anything (not even res = ...) in front of that command.

However you still need the -o because otherwise the _ variable contains None.

Answer 2

If you just care about the output of the cell magic, e.g. for recording purposes - and you don't need the extra metadata included in the TimeitResult object, you could also just combine it with %%capture:

%%capture result
%%timeit

A = np.mat('1 2 3; 7 4 9; 5 6 1')
np.linalg.inv(A)

Then you can grab the output from result.stdout, which will yield whatever the output of the cell is - including the timing result.

print(result.stdout)

'26.4 us +- 329 ns per loop (mean +- std. dev. of 7 runs, 10000 loops each)\n'

This works for arbitrary cell magic, and can work as a fallback if the underscore solution isn't working.