PYTHON STACK FUNCTION count the valid number of brackets Returns the total number of valid brackets in the string

import sys

def error(c, line_number, column_number):

    print ‘Error: unmatched’, c, ‘line’, line_number, ‘column’, column_number
def check(stack, wanted, c, line_number, column_number):

    if stack[-1] != wanted:

        error(c, line_number, column_number)

    else:

        stack.pop()
def check_parentheses(f):

    stack = list()

    line_number = 0

    for line in f:

        line_number = line_number + 1

        column_number = 0

        for c in line:

            column_number = column_number + 1

            if c == ‘(‘ or c == ‘[‘ or c == ‘{‘:

                stack.append(c)

            elif c == ‘)’:

                check(stack, ‘(‘, ‘)’, line_number, column_number)

            elif c == ‘]’:

                check(stack, ‘[‘, ‘]’, line_number, column_number)

            elif c == ‘}’:

                check(stack, ‘{‘, ‘}’, line_number, column_number)
def main():

    filename = sys.argv[1]

    try:

        f = file(filename)

    except IOError:

        sys.stderr.write(‘Error: Cannot open file %s’ % filename)

        sys.exit(1)

    check_parentheses(f)

    f.close()
main()