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| def verify_balanced(s): | |
| """Verifies that all '{', '[', and '(' characters have closing partners. | |
| Returns: | |
| the index of an out of first unbalanced character or `None` | |
| Doctests: | |
| >>> verify_balanced('asdf (foo) [bar] [[baz], {}, ()]') | |
| None | |
| >>> verify_balanced('asdf )foo [bar] [[baz], {}, ()]') | |
| 5 | |
| """ | |
| opening = '{[(' | |
| closing = '}])' | |
| stack = [] | |
| for i, c in enumerate(s): | |
| if c in opening: | |
| stack.append((i, opening.index(c))) | |
| elif c in closing: | |
| if len(stack) == 0: | |
| return i | |
| j, x = stack.pop() | |
| if x != closing.index(c): | |
| return j | |
| if len(stack) > 0: | |
| j, x = stack.pop() | |
| return j | |
| return None |
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