Evaluate reverse polish notation

/*
Logic:
push numbers into stack and whenever operators comes pop top two items
and operate on them and push the result.
*/
class Solution:
    def evalRPN(self, tokens: List[str]) -> int:
        st=[]
        for i in tokens:
            if i.isdigit() or (i[1:].isdigit() and i[0]=='-'):
                st.append(int(i))
            else:
                a=st.pop()
                b=st.pop()
                if i=='+':
                    st.append(a+b)
                elif i=='-':
                    st.append(b-a)
                elif i=='*':
                    st.append(a*b)
                else:
                    st.append(int(b/a))
        return st[0]