def swap_pair(pair):
    """ Return array of first two elements swapped. """
    return [pair[1], pair[0]]

a = [10, 20]
print "original: " + str(a)
b = swap_pair(a)
print "modified: " + str(b)

print swap_pair([101, 102])

# - - - - - - - - - - -

def swap_in_place(pair):
    """ Swap first two elements in place """
    temp = pair[0]
    pair[0] = pair[1]
    pair[1] = temp

a = [10, 20]
print "original: " + str(a)
swap_in_place(a)
print "modified: " + str(a)

swap_in_place([101, 102])    # DON'T DO THIS