Element-wise string concatenation in numpy

This can be done using numpy.core.defchararray.add. Here is an example:

>>> import numpy as np
>>> a1 = np.array(['a', 'b'])
>>> a2 = np.array(['E', 'F'])
>>> np.core.defchararray.add(a1, a2)
array(['aE', 'bF'], 
      dtype='<U2')

There are other useful string operations available for NumPy data types.

This can (and should) be done in pure Python, as numpy also uses the Python string manipulation functions internally:

>>> a1 = ['a','b']
>>> a2 = ['E','F']
>>> map(''.join, zip(a1, a2))
['aE', 'bF']

You can use the chararray subclass to perform array operations with strings:

a1 = np.char.array(['a', 'b'])
a2 = np.char.array(['E', 'F'])

a1 + a2
#chararray(['aE', 'bF'], dtype='|S2')

another nice example:

b = np.array([2, 4])
a1*b
#chararray(['aa', 'bbbb'], dtype='|S4')