gistfile1.py

import timeit
import numpy
import scipy.ndimage.morphology

def f0(a, kernel):
    b = numpy.convolve(a, kernel, mode="same") > 1
    b[1:] |= b[:-1]
    b[:-1] |= b[1:]
    return b

def f1(a, kernel):
    b = numpy.convolve(a, kernel, mode="same") > 1
    return b | numpy.r_[0, b[:-1]] | numpy.r_[b[1:], 0]

def f2(a, kernel):
    b = numpy.convolve(a, kernel, mode="same") > 1
    return numpy.convolve(b, kernel, mode="same") > 0

def f3(a, kernel):
    b = numpy.convolve(a, kernel, mode="same") > 1
    return scipy.ndimage.morphology.binary_dilation(b)

def f4(a, kernel):
    b = numpy.zeros(a.shape)
    for x in range(len(a)-2):
        if a[x:x+3].sum()>1:
            b[x:x+3]=1
    return b

a = numpy.random.randint(2, size=1000000)
kernel = numpy.array([1, 1, 1])
for i in range(5):
    fname = "f" + str(i)
    print timeit.timeit(fname + "(a, kernel)",
                        "from __main__ import a, kernel, " + fname,
                        number=10)