math.tau (PEP-628)

The issue with a beautiful number #12345 proposed to add the following constant into stdlib:

tau = 2*math.pi

It was a controversial proposal since apparently it's not hard to recreate this constant on your own which will be more explicit, since more people are familiar with π rather than τ. However, the proposal was accepted and tau landed in math module in Python 3.6 (PEP-628):

import math
math.tau
# 6.283185307179586

There is a long story behind τ which you can read at tauday.com. Especially good this numberphile video.