Why is numpy.array() is sometimes very slow?

Question

I\'m using the numpy.array() function to create numpy.float64 ndarrays from lists.

I noticed that this is very slow when either the list contains None or a list of l

Answer 1

I've reported this as a numpy issue. The report and patch files are here:

https://github.com/numpy/numpy/issues/3392

After patching:

# was 240 ms, best alternate version was 3.29
In [5]: %timeit numpy.array([None]*100000)
100 loops, best of 3: 7.49 ms per loop

# was 353 ms, best alternate version was 9.65
In [6]: %timeit numpy.array([[0.0]]*100000)
10 loops, best of 3: 23.7 ms per loop