while(old_password!=self.password_str):
    AttributeError: 'Player' object has no attribute 'password_str'

class Player(object):

def __init__(self, username_str="-", password_str=""):
    while (not validated(password_str)):
        self.password_str=input("Password is invalid. Please try again:")
        self.username=username_str

def change_password(self,old_password):
    MAX_ATTEMPT=3
    num_of_fails=0
    while(old_password!=self.password_str):
        num_of_fails+=1
        if(num_of_fails<MAX_ATTEMPT):
            old_password=input("Thej passwword entered is invalid. Please try again.
            (You have "+str(MAX_ATTEMPT-num_of_fails)+" attempts reamining)")
        else:
            print("Incorrect password entered too many times. Your account is temporarily locked.")
            break

    if(num_of_fails<MAX_ATTEMPT):
        new_password=input("please enter a new password.")

        while(not validated(new_password)):
            new_password=input("New password is invalid. Please try again")

        self.password_str=new_password
        print("Password has been successfully changed!")