human
Solve the following python programming problem given the following code:
def authenticate(self, username, password) : 
    user = None 
    try : 
        auth = PAM.pam () 
        def pam_conv(auth, query_list, userData) : 
            response = [] 
            for i in range (len (query_list)) : 
                (query, type) = query_list [i] 
                if (type == PAM.PAM_PROMPT_ECHO_ON) : 
                    val = raw_input (query) 
                    response.append ((val, 0)) 
else : 
                    if (type == PAM.PAM_PROMPT_ECHO_OFF) : 
                        response.append ((password, 0)) 
else : 
                        if ((type == PAM.PAM_PROMPT_ERROR_MSG) or (type == PAM.PAM_PROMPT_TEXT_INFO)) : 
                            response.append (('', 0)) 
else : 
                            return None 
return response 
auth.start (self.PAM_SERVICE) 
        auth.set_item (PAM.PAM_USER, username) 
        auth.set_item (PAM.PAM_CONV, pam_conv) 
        try : 
            auth.authenticate () 
            auth.acct_mgmt () 
            user = { 
                'username' : username, 
                'name' : username, 
                'su' : 'Yes', 
} 
except PAM.error : 
            pass 
except NameError : 
        p = pam_m 
        if p.authenticate (username, password, service = self.PAM_SERVICE) : 
            user = { 
                'username' : password, 
                'name' : username, 
                'su' : 'Yes', 
} 
return user 

    
    

    Fix the buggy line: 'username' : password ,
assistant
#Here is Python code to fix the buggy line: 'username' : password ,
.

'username' : username ,