A classic stack problem: are the brackets in a piece of text balanced? Every ( needs a ), every [ a ], and they must close in the right order: ([]) is fine, ([)] isn't.

The trick: push each opening bracket; when you meet a closing one, the top of the stack must be its partner.

def balanced(text):
    pairs = {")": "(", "]": "[", "}": "{"}
    stack = []
    for ch in text:
        if ch in "([{":
            stack.append(ch)
        elif ch in pairs:
            if not stack or stack.pop() != pairs[ch]:
                return False
    return not stack

for t in ["(a[b]c)", "([)]", "((", "f(x) = {1, 2}"]:
    print(t, balanced(t))

At the end, the stack must be empty: anything left is an opening bracket that never closed.