Here is one way to do it
>>> s1 = "abc"
>>> s2 = "xyz"
>>> "".join(i for j in zip(s1, s2) for i in j)
'axbycz'
It also works for more than 2 strings
>>> s3 = "123"
>>> "".join(i for j in zip(s1, s2, s3) for i in j)
'ax1by2cz3'
Here is another way
>>> "".join("".join(i) for i in zip(s1,s2,s3))
'ax1by2cz3'
And another
>>> from itertools import chain
>>> "".join(chain(*zip(s1, s2, s3)))
'ax1by2cz3'
And one without zip
>>> b = bytearray(6)
>>> b[::2] = "abc"
>>> b[1::2] = "xyz"
>>> str(b)
'axbycz'
And an inefficient one
>>> ((s1 + " " + s2) * len(s1))[::len(s1) + 1]
'axbycz'