For short arrays, using sets is probably the clearest and most readable way to do it.

Another way is to use numpy.intersect1d. You'll have to trick it into treating the rows as a single value, though... This makes things a bit less readable...

import numpy as np

A = np.array([[1,4],[2,5],[3,6]])
B = np.array([[1,4],[3,6],[7,8]])

nrows, ncols = A.shape
dtype={'names':['f{}'.format(i) for i in range(ncols)],
       'formats':ncols * [A.dtype]}

C = np.intersect1d(A.view(dtype), B.view(dtype))

# This last bit is optional if you're okay with "C" being a structured array...
C = C.view(A.dtype).reshape(-1, ncols)

For large arrays, this should be considerably faster than using sets.

This should do it:

In [11]:

def f(arrA, arrB):
    return not set(map(tuple, arrA)).isdisjoint(map(tuple, arrB))
In [12]:

f(A, B)
Out[12]:
True
In [13]:

f(A, C)
Out[13]:
False
In [14]:

f(B, C)
Out[14]:
False

To find intersection? OK, set sounds like a logical choice. But numpy.array or list are not hashable? OK, convert them to tuple. That is the idea.

A numpy way of doing involves very unreadable boardcasting:

In [34]:

(A[...,np.newaxis]==B[...,np.newaxis].T).all(1)
Out[34]:
array([[False, False],
       [ True, False],
       [False, False]], dtype=bool)
In [36]:

(A[...,np.newaxis]==B[...,np.newaxis].T).all(1).any()
Out[36]:
True

Some timeit result:

In [38]:
#Dan's method
%timeit set_comp(A,B)
10000 loops, best of 3: 34.1 µs per loop
In [39]:
#Avoiding lambda will speed things up
%timeit f(A,B)
10000 loops, best of 3: 23.8 µs per loop
In [40]:
#numpy way probably will be slow, unless the size of the array is very big (my guess)
%timeit (A[...,np.newaxis]==B[...,np.newaxis].T).all(1).any()
10000 loops, best of 3: 49.8 µs per loop

Also the numpy method will be RAM hungry, as A[...,np.newaxis]==B[...,np.newaxis].T step creates a 3D array.

The main optimization I can think of is precomputing the sets. If array1 has shape [m,n] and array2 is [q,p], the original code is creating a set 2*m*q times. You can get this down to m+q.

In addition, you could follow the Python style guide in terms of naming conventions and whitespace, which will help working together with other Python programmers. Also it's nice to loop over the data structure itself instead of over a range of indices.

This would result in for example:

import numpy as np

def intersection(array1, array2):
    intersection = np.empty([array1.shape[0], array2.shape[0]], dtype=np.int8)
    array2_sets = map(set, array2)
    for i,row1 in enumerate(array1):
        set1 = set(row1)
        for j, set2 in enumerate(array2_sets):
            intersection[i,j] = len(set1.intersection(set2))
    return intersection

If you can forget about "keeping it simple to understand" you could also convert your data to sparse matrices and take the matrix product, e.g.:

from scipy.sparse import csr_matrix

def intersection2(A, B, sparse=True):
    """The rows of A and B must contain unique, relatively 
    small integers
    """
    assert min(A.shape[1], B.shape[1]) < 256  # to fit inside uint8
    z = max(A.max(), B.max()) + 1

    def sparsify(A):
        m, n = A.shape
        indptr = np.arange(0, m*n+1, n)
        data = np.ones(m*n, dtype=np.uint8)
        return csr_matrix((data, A.ravel(), indptr), shape=(m,z))

    intersection = sparsify(A) * sparsify(B).T
    return intersection if sparse else intersection.todense()