将数学表达式转化成树结构

def from_infix_to_prefix(expression):
    st = list()
    res = list()
    priority = {"+": 0, "-": 0, "*": 1, "/": 1, "^": 2}
    expression = deepcopy(expression)
    expression.reverse()
    for e in expression:
        if e in [")", "]"]:
            st.append(e)
        elif e == "(":
            c = st.pop()
            while c != ")":
                res.append(c)
                c = st.pop()
        elif e == "[":
            c = st.pop()
            while c != "]":
                res.append(c)
                c = st.pop()
        elif e in priority:
            while len(st) > 0 and st[-1] not in [")", "]"] and priority[e] < priority[st[-1]]:
                res.append(st.pop())
            st.append(e)
        else:
            res.append(e)
    while len(st) > 0:
        res.append(st.pop())
    res.reverse()
    return res

['(', 'N1', '-', '1', ')', '*', 'N0'] -> ['*', '-', 'N1', '1', 'N0']
先反转是为了得到先序遍历 根左右，不然就会成为根右左