Valid parentheses

class Solution:
   def isValid (self, sequence: str):
       '''
       Function to pair if sequence contains valid parenthesis
       :param sequence: Sequence of brackets
       :return: True is sequence is valid else False
       '''
       stack = []
       opening = set('([{')
       closing = set(')]}')
       pair = {')' : '(' , ']' : '[' , '}' : '{'}
       for i in sequence :
           if i in opening :
               stack.append(i)
           if i in closing :
               if not stack :
                   return False
               elif stack.pop() != pair[i] :
                   return False
               else :
                   continue
       if not stack :
           return True
       else :
           return False

if __name__ == '__main__':
   sequence = '{[()]}'
   print(f'Is {sequence} valid ? : {Solution().isValid(sequence)}')
   sequence1 = '{[()]}{]{}}'
   print(f'Is {sequence1} valid ? : {Solution().isValid (sequence1)}')

Source: favtutor.com

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()

Source: stackoverflow.com

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