human
Solve the following python programming problem given the following code:
@ gen.coroutine 
def ListIdentities(client, obj_store, user_id, device_id, request) : 
    'Returns a list of identities linked to this account.' 
    def _MakeIdentityDict(ident) : 
        i_dict = { 
            'identity' : ident.key, 
} 
        if (ident.authority is not None) : 
            i_dict ['authority'] = ident.authority 
return i_dict 
query_expr = ('identity.user_id=%d' % identities) 
    identities = (yield gen.Task (Identity.IndexQuery, client, query_expr, ['key', 'authority'])) 
    raise gen.Return ({ 
        'identities' : [_MakeIdentityDict (ident) for ident in identities], 
}) 

    
    

    Fix the buggy line: query_expr = ('identity.user_id=%d' % identities)
assistant
#Here is Python code to fix the buggy line: query_expr = ('identity.

query_expr = ('identity.user_id=%d' % user_id)