Add Base85 encoding support for Python 3

[dargueta]

TL;DR: Allow using Base85 text encoding on Python 3.

Details

This doesn't remove base64 encoding support for Python 3; rather, it makes base85 the default but still allows overriding the default to only use base64 for backwards compatibility with Python 2. (Python 2 doesn't support base85, nor does there appear to be a backport for it.)

Why

It's a more compact text encoding than Base64, and some manual experimentation gives about a 10% space savings for randomized binary data.

Closes #250.

[davvid]

Sweet, this looks perfect except for one little trivial tweak that I'll fixup here before pushing out the merge. I'm going to rename the variables from prefer_base85 to use_base85, for consistency with the existing use_decimal.

[cyberic99]

Hi,

Has anyone done any perf mesurement after switching to base85?

[dargueta]

Oh, good point. All of my testing has been on relatively simple stuff.

Update

base85 appears to be slower on Python 3.6 and 3.7 by a factor of about 2.25. 😬 Maybe it should be an opt-in feature. (Base64 is implemented in C, base85 in Python.)

[davvid]

We haven't tagged a release yet so changing this default is still fair game.

[dargueta]

I looked at the Python 3.6 source code and it appears that there's significant overhead on the first call to b85encode because it builds some tables, but subsequent calls are faster. Still, it's noticeably slower than base64.

I'll open a PR to switch base64 to be the default later today. Thanks @cyberic99 for pointing out something I obviously should've done first. Sorry about this!

[dargueta]

Done: #252

[cyberic99]

Thx @dargueta !

For my use case, the thoughput is more important than the file size, so I thought about the performance impact right away ;-)