balancedparentheses.py

"""
    balancedparentheses.py
    Program to check for balanced parentheses in an expression using stack
    To run you only need Python3 installed
    
    To exectue:
    python3 balancedparentheses.py
 
    modified from the code here: http://www.lifengadget.com/lifengadget/program-to-check-for-balanced-parentheses-in-an-expression/
"""

def bracketsame(opening,closing): # function checks if opening and closing brackets are same
    if(opening == '(' and closing == ')') :
        return True
    elif(opening == '{' and closing == '}'): 
        return True
    elif(opening == '[' and closing == ']') :
        return True
        
    return False

def balancedparantheses(exp): #checks if parentheses are balanced or not
    stack = []
    for c in exp:
        if(c == '(' or c == '{' or c == '['):
            stack.append(c)
        elif(c == ')' or c == '}' or c == ']'):
            if(len(stack) == 0 or not bracketsame(stack[-1],c)):
                return False
            else:
                stack.pop(len(stack)-1)
                
    if len(stack) == 0:
        return True
    else:
        return False
 
 
# =========================================================
# main
getOut = False

while getOut == False:
    expression = input("Enter an expression to check: ")
    if(balancedparantheses(expression)):
        print("Balanced expression \n")
    else:
        print("Expression is not balanced \n")
    userEntered = input("press q to exit, any key to continue:")
    if userEntered.lower() == 'q':
        getOut = True
        print('user exiting')
    else:
        getOut = False