How to add a new row to an empty numpy array

Question

Using standard Python arrays, I can do the following:

arr = []
arr.append([1,2,3])
arr.append([4,5,6])
# arr is now [[1,2,3],[4,5,6]]

Howev

Answer 1

In case of adding new rows for array in loop, Assign the array directly for firsttime in loop instead of initialising an empty array.

for i in range(0,len(0,100)):
    SOMECALCULATEDARRAY = .......
    if(i==0):
        finalArrayCollection = SOMECALCULATEDARRAY
    else:
        finalArrayCollection = np.vstack(finalArrayCollection,SOMECALCULATEDARRAY)

This is mainly useful when the shape of the array is unknown