np.memap won't work without mode parameter if the file does not exist yet (receipe 4.9)

[rndblnch]

the memory mapping exemple will only work if the file already exists.
to make it work regardless of that, it should have the mode parameter filled:

f = np.memmap('memmapped.dat', dtype=np.float32, mode='w+', shape=(nrows, ncols))

https://github.com/ipython-books/cookbook-code/blob/master/notebooks/chapter04_optimization/09_memmap.ipynb#L61

[rossant]

Thanks! PR welcome :)