src_array[:, 3] += column_array_to_add[:, 0]

import numpy
src = numpy.array([["a", "b"], ["c", "d"], ["e", "f"]])
src2 = numpy.array([["x"], ["y"], ["z"]])

src[:, 1] += src2[:, 0]
print src
exit()

src[:, 1] += src2[:, 0]

import numpy as np

x = np.array([[1,2],[3,4]])

y = np.array([[5,6],[7,8]])

>>> x
array([[1, 2],
       [3, 4]])
>>> y
array([[5, 6],
       [7, 8]])
>>> x[:,1] + y[:,1]
array([ 8, 12])
>>> x[:, 1] += y[:, 1] # using +=
>>> x[:, 1]
array([ 8, 12])

src = np.array([["a", "b"], ["c", "d"], ["e", "f"]], dtype='|S8')
src2 = np.array([["x"], ["y"], ["z"]], dtype='|S8')

def add_columns(x, y):
    return [a + b for a,b in zip(x, y)]

def update_array(source_array, col_num, add_col):
    temp_col = add_columns(source_array[:, col_num], add_col)
    source_array[:, col_num] = temp_col
    return source_array

>>> update_array(src, 1, src2[:,0])
array([['a', 'bx'],
       ['c', 'dy'],
       ['e', 'fz']],
      dtype='|S8')

>>> src[:, 1]
array(['b', 'd', 'f'], dtype='|S1')
>>> src[:, 1] = ['x', 'y', 'z']
>>> src
>>> array([['a', 'x'], ['c', 'y'], ['e', 'z']], dtype='|S1')

>>> src + src2
TypeError: unsupported operand type(s) for +: 'numpy.ndarray' and 'numpy.ndarray'

>>> s1, s2 = np.array('a'), np.array('b')
>>> s1 + s2
TypeError: unsupported operand type(s) for +: 'numpy.ndarray' and 'numpy.ndarray'

>>> n1, n2 = np.array(1), np.array(2)
>>> n1 + n2
3

>>> m1 = np.array([[1,2], [3,4], [5,6]])
>>> m2 = np.array([[7], [8], [9]])
>>> m1[:, 1] += m2[:, 0]
>>> array([[ 1,  9],
           [ 3, 12],
           [ 5, 15]])

>>> src = numpy.array([["a", "b"], ["c", "d"], ["e", "f"]])
>>> src
array([['a', 'b'], ['c', 'd'], ['e', 'f']], dtype='|S1')

>>> src = numpy.array([["a", "b"], ["c", "d"], ["e", "f"]], dtype=object)
>>> src2 = numpy.array([["x"], ["y"], ["z"]], dtype=object)
>>> src[:, 1] += src2[:, 0]