Valid Parentheses

class Solution:
    def isValid(self, s: str) -> bool:
        # Use list to represent stack
        stk = []

        # Loop through string
        for c in s:
            # If opening paren, push paren onto stack
            if c == '(' or c == '[' or c == '{':
                stk.append(c)
            # If closing paren
            elif c == ')' or c == ']' or c == '}':
                # If stack is empty, return False
                if not stk:
                    return False
                # If top elem on stack is matching open paren, pop open paren from stack
                if (c == ')' and stk[-1] == '(') or (c == ']' and stk[-1] == '[') or (c == '}' and stk[-1] == '{'):
                    stk.pop()
                # Else, return False
                else:
                    return False

        # If stack is empty return True, else return False
        if not stk:
            return True
        return False