Encryption and Decryption using Variable Caesar Cipher - System Security | Python3

a=input("Enter the msg: ")
ct=[]
pt=[]
y=2
x=0
key=0
z=3
k=0

for i in a:
    key=int(2*x+3*y+z)
    if ord(i)>=97 and ord(i)<=122:
        d=(((ord(i)+key)-97)%26)+97
        ct.append(chr(d))        
    elif ord(i)>=62 and ord(i)<=90:
        d=(((ord(i)+key)-62)%26)+62
        ct.append(chr(d))
    else:
        ct.append(i)
    x=x+1
    key=0
        
print ("\nEncrypted Data")
str1 = ''.join(ct)
print (str1)

for i in ct:
    key=2*k+3*y+z
    if ord(i)>=97 and ord(i)<=122:    
        d=(((ord(i)-key)-97)%26)+97
        pt.append(chr(d))   
    elif ord(i)>=62 and ord(i)<=90:
        d=(((ord(i)-key)-62)%26)+62
        pt.append(chr(d))
    else:
        pt.append(i)
    key=0
    k=k+1
            
print ("\nDecrypted Data")
str2 = ''.join(pt)
print (str2)

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