Bytes and Strings Rear Their Ugly Heads Again

The pickle protocol has been around for many years, and it has matured as Python itself has matured. There are now four different versions of the pickle protocol.

• Python 1.x had two pickle protocols, a text-based format (“version 0”) and a binary format (“version 1”).
• Python 2.3 introduced a new pickle protocol (“version 2”) to handle new functionality in Python class objects. It is a binary format.
• Python 3.0 introduced another pickle protocol (“version 3”) with explicit support for bytes objects and byte arrays. It is a binary format.

Oh look, the difference between bytes and strings rears its ugly head again. (If you’re surprised, you haven’t been paying attention.) What this means in practice is that, while Python 3 can read data pickled with protocol version 2, Python 2 can not read data pickled with protocol version 3.