Numpy
From charlesreid1
Arrays
Initializing an empty array
Sometimes you want to initalize an empty array, which is a really inefficient use of memory for large matrices but you could care less if it's a dozen items.
In [62]: x=[]
In [63]: x=np.array(x)
In [64]: x
Out[64]: array([], dtype=float64)
In [66]: x = np.array([],dtype=np.float64)
In [67]: x
Out[67]: array([], dtype=float64)