check redundant braces in valid math expression

https://www.codingninjas.com/codestudio/problems/redundant-brackets_975473?leftPanelTab=1
def findRedundantBrackets(s:str):
    st=[]
    if s=='':return False
    sym='(+-/*' #no close brack
    for i in s:
        if i in sym :#any other symb than close br
            st.append(i)
        elif i==')':
            if st[-1]=='(':
                return True
            else:
                while st[-1]!='(':st.pop()
            st.pop()
        else:
            continue #skipping variables
    return False