---
title: "ByteByteGo: Valid Parenthesis Expression"
url: https://perrotta.dev/2025/11/bytebytego-valid-parenthesis-expression/
last_updated: 2026-01-03
---


[ByteByteGo: Valid Parenthesis Expression](https://bytebytego.com/exercises/coding-patterns/stacks/valid-parenthesis-expression):

```python
def valid_parenthesis_expression(s: str) -> bool:
    stack = []

    for c in s:
        if c in '([{':
            stack.append(c)

        if len(stack) == 0:
            return False

        if c == ')':
            if stack.pop() != '(':
                return False

        if c == ']':
            if stack.pop() != '[':
                return False

        if c == '}':
            if stack.pop() != '{':
                return False

    return len(stack) == 0
```

Refinement:

```python
def valid_parenthesis_expression(s: str) -> bool:
    stack = []

    ass = {
        ')': '(',
        ']': '[',
        '}': '{',
    }

    for c in s:
        if c in '([{':
            stack.append(c)

        if len(stack) == 0:
            return False

        if c in ')]}':
            if stack.pop() != ass[c]:
                return False

    return len(stack) == 0
```