def __add__(self, other):
        if not isinstance(other, Counter):
            return NotImplemented
        result = Counter()
        for elem, count in self.items():
            newcount = count + other[elem]
            if newcount > 0:
                result[elem] = newcount
        for elem, count in other.items():
            if elem not in self and count > 0:
                result[elem] = count
        return result
Add counts from two counters.
dataset/ETHPy150Open Exa-Networks/exabgp/lib/exabgp/dep/counter.py/Counter.__add__