There are two issues. The one is that calculated Content-Length is not correct for lists, tuples, and other types (such as deque or array.array). The right solution is to calculate size using a technique used in urllib. Content-Length shouldn't be calculated for lists, tuples, and other non-bytes-compatible sequences. This is a bug, and the patch should be applied to all maintained releases.

The second issue is feature request. Allow calculating Content-Length for lists and tuples.