KnowledgeBasedPrepositionalLogic.py

combinations=[(True,True),(False,False),(False,True),(True,False)]
variable={'p':0,'q':1}
kb=''
q=''
priority={'~':3,'v':1,'^':2}
def input_rules():
    global kb,q
    kb=(input("Enter rule  :"))    
    q=input("Enter the Query : ")    

def entailment():
    global kb,q
    print('*'*10+"Truth Table Reference"+'*'*10)
    print('kb','alpha')
    print('*'*10)
    for comb in combinations:
        s=evaluatePostfix(toPostfix(kb),comb)
        f=evaluatePostfix(toPostfix(q),comb) 
        print(s,f) 
        print('-'*10)     
        if s and not f:            
            return False
    return True

def isOperand(c):
    return c.isalpha() and c!='v'

def isLeftParenthesis(c):
    return c=='('
def isRightParenthesis(c):
    return c==')'
def isEmpty(stack):
    return len(stack)==0

def peek(stack):
     return stack[-1]

def hasLessOrEqualPriority(c1,c2):
     try: return priority[c1]<=priority[c2]
     except KeyError: return False

def toPostfix(infix):
    stack = []
    postfix = ''
    for c in infix:
        if isOperand(c):
            postfix += c
        else:
            if isLeftParenthesis(c):
                stack.append(c)
            elif isRightParenthesis(c):
                operator = stack.pop()
                while not isLeftParenthesis(operator):
                    postfix += operator
                    operator = stack.pop()              
            else:
                while (not isEmpty(stack)) and hasLessOrEqualPriority(c,peek(stack)):
                    postfix += stack.pop()
                stack.append(c)

    while (not isEmpty(stack)):
        postfix += stack.pop()
    return postfix

def evaluatePostfix(exp,comb):          
        stack=[]
        for i in exp:              
            if isOperand(i): 
                stack.append(comb[variable[i]])
            elif i=='~':
                val1 = stack.pop()
                stack.append(not val1)                    
            else:
                val1 = stack.pop()
                val2 = stack.pop() 
                stack.append(_eval(i,val2,val1)) 
  
        return stack.pop()

def _eval(i,val1,val2):
    if i=='^': return val2 and val1
    return val2 or val1   

input_rules()
ans=entailment()
if ans: print("The Knowlege Base entails query ")
else: print("The Knowlege Base does not entail query ")