Fetch nested bracketed values from string

nested_bracketed_values.py

template = """head{var1}middle{var2{nested}}end"""

def parenthetic_contents(string):
    """Generate parenthesized contents in string as pairs (level, contents)."""
    stack = []
    for i, c in enumerate(string):
        if c == '{':
            stack.append(i)
        elif c == '}' and stack:
            start = stack.pop()
            yield (len(stack), string[start + 1: i])

list(parenthetic_contents(template))
# [(0, 'var1'), (1, 'nested'), (0, 'var2{nested}')]