Password Encryption Help Python3

[SockMankey]

I am trying to make a program that is given a password and encrypts it by shifting each value up by 3. For example, if you entered in the password: Ab1 you would get De4. I'm trying to make it to where if the input is Z or 9, the output loops back to the start. So the password for Z9 would be C3.
I know I need to have a loop in order to accomplish this, but I'm not sure which type of loop/where to put the loop.

def caesar(text):
    ciphertext=""
    for char in text:
        if char.isupper():
            ciphertext += chr((ord(char)+3 -65)%+26+65)
        elif char.islower():
            ciphertext += chr((ord(char)+3-97)%26+97)
        elif char.isdigit():
            ciphertext += chr((ord(char)+3))
        else:
            ciphertext+=char
    return ciphertext
text = input("Enter a password: ")
print('Plain Text: ', text)
print('Cipher:', caesar(text))