How do you check for valid/balanced parentheses?

Question presented to candidate: "Given a string that contains only the characters ( ) [ ] { }, write a Python function that returns True if every bracket is closed by the same kind of bracket in the correct order, and False otherwise. Talk me through the edge cases."

What a strong answer should cover:

• Use a stack because the most recently opened bracket must close first (last in, first out).
• The three failure cases: a closer with an empty stack, a closer that does not match the top, and openers left over at the end.
• O(n) time and O(n) space, with the early exit on odd length and on the first mismatch.
• Why a single counter only works for one bracket type: it cannot see order, so ([)] slips through.
• Python specifics: a list used as a stack with append, pop and stack[-1]; a dict mapping closer to opener; stack.pop() on an empty list raises IndexError, so check not stack first.

Clarifying questions expected:

• "Can the string contain characters other than brackets?"
• "Should an empty string count as valid?"

Code / implementation expected: Yes — a short Python function using a list as the stack and a dict of pairs.