balanced_delimeters.py

#!/usr/bin/python

def has_balanced_delimiters(string, delimiters={'(': ')', '[': ']', '{': '}'}):
    """
    Parses a string to determine if it contains balanced delimiters.

    A balanced delimiter string starts with an opening character ((, [, {), ends
    with a matching closing character (), ], } respectively). A balanced
    delimiter string may contain any number of balanced delimiters.
    """
    stack = []
    for char in string:
        if char in delimiters:
            stack.append(char)

        if char in delimiters.values():
            if stack and char == delimiters[stack[-1]]:
                stack.pop()
            else:
                return False

    return False if stack else True


if __name__ == '__main__':
    strings = [
        '(){}',
        '([{}])',
        '({})',
        '([)]',
        '(',
        ')',
        '([})',
        '())',
        '[(2 + 2) * (42 - 42)] / {3.14}',
        '[(2 + 2) * (42 - 42)] / {3.14'
    ]

    for string in strings:
        print '"{}" {} balanced delimiters'.format(
            string, 'has' if has_balanced_delimiters(string) else 'does not have')