Find and Replace First Dot.

parser.py

matching = {
    '{': '}',
    '(': ')'
}

def find_first_dot(line):
    paren_stack = []

    for pos, ch in enumerate(line):
        if ch in matching:
            paren_stack.append(ch)

        else:
            if paren_stack: 
                if ch == matching[paren_stack[-1]]:
                    paren_stack.pop()
            else:
                if ch == '.':
                    return pos

    return -1

            
for line in open("sample-text.txt"):
    print line

    pos = find_first_dot(line)
    if pos != -1:
        line = list(line)
        line[pos] = '#'
        line = "".join(line)

    print line