Using XOR:

```
class Solution(object):
def findTheDifference(self, s, t):
return chr(reduce(operator.xor, map(ord, s + t)))
```

Using `collections.Counter()`

:

```
class Solution(object):
def findTheDifference(self, s, t):
return list((collections.Counter(t) - collections.Counter(s)))[0]
```

A 2-liner here using `sorted()`

:

```
class Solution(object):
def findTheDifference(self, s, t):
s, t = sorted(s), sorted(t)
return t[-1] if s == t[:-1] else [x[1] for x in zip(s, t) if x[0] != x[1]][0]
```