def make_atom(self, child, qn, connection):
        lvalue, lookup_type, value_annotation, params_or_value = child
        if isinstance(lvalue, Constraint):
            try:
                lvalue, params = lvalue.process(lookup_type, params_or_value, connection)
            except EmptyShortCircuit:
                raise EmptyResultSet
        elif isinstance(lvalue, Aggregate):
            params = lvalue.field.get_db_prep_lookup(lookup_type, params_or_value, connection)
        else:
            raise TypeError("'make_atom' expects a Constraint or an Aggregate "
                            "as the first item of its 'child' argument.")

        if isinstance(lvalue, tuple):
            # A direct database column lookup.
            field_sql = self.sql_for_columns(lvalue, qn, connection)
        else:
            # A smart object with an as_sql() method.
            field_sql = lvalue.as_sql(qn, connection)

        if value_annotation is datetime.datetime:
            cast_sql = connection.ops.datetime_cast_sql()
        else:
            cast_sql = '%s'

        if hasattr(params, 'as_sql'):
            extra, params = params.as_sql(qn, connection)
            cast_sql = ''
        else:
            extra = ''

        if (len(params) == 1 and params[0] == '' and lookup_type == 'exact'
            and connection.features.interprets_empty_strings_as_nulls):
            lookup_type = 'isnull'
            value_annotation = True

        if lookup_type in connection.operators:
            format = "%s %%s %%s" % (connection.ops.lookup_cast(lookup_type),)
            return (format % (field_sql,
                              connection.operators[lookup_type] % cast_sql,
                              extra), params)

        if lookup_type == 'in':
            if not value_annotation:
                raise EmptyResultSet
            if extra:
                return ('%s IN %s' % (field_sql, extra), params)
            max_in_list_size = connection.ops.max_in_list_size()
            if max_in_list_size and len(params) > max_in_list_size:
                # Break up the params list into an OR of manageable chunks.
                in_clause_elements = ['(']
                for offset in xrange(0, len(params), max_in_list_size):
                    if offset > 0:
                        in_clause_elements.append(' OR ')
                    in_clause_elements.append('%s IN (' % field_sql)
                    group_size = min(len(params) - offset, max_in_list_size)
                    param_group = ', '.join(repeat('%s', group_size))
                    in_clause_elements.append(param_group)
                    in_clause_elements.append(')')
                in_clause_elements.append(')')
                return ''.join(in_clause_elements), params
            else:
                return ('%s IN (%s)' % (field_sql,
                                        ', '.join(repeat('%s', len(params)))),
                        params)
        elif lookup_type in ('range', 'year'):
            return ('%s BETWEEN %%s and %%s' % field_sql, params)
        elif lookup_type in ('month', 'day', 'week_day'):
            return ('%s = %%s' % connection.ops.date_extract_sql(lookup_type, field_sql),
                    params)
        elif lookup_type == 'isnull':
            return ('%s IS %sNULL' % (field_sql,
                (not value_annotation and 'NOT ' or '')), ())
        elif lookup_type == 'search':
            return (connection.ops.fulltext_search_sql(field_sql), params)
        elif lookup_type in ('regex', 'iregex'):
            return connection.ops.regex_lookup(lookup_type) % (field_sql, cast_sql), params

        raise TypeError('Invalid lookup_type: %r' % lookup_type)
Turn a tuple (Constraint(table_alias, column_name, db_type),
dataset/ETHPy150Open daoluan/decode-Django/Django-1.5.1/django/db/models/sql/where.py/WhereNode.make_atom