PEP 628 – Add
- Alyssa Coghlan <ncoghlan at gmail.com>
- Standards Track
In honour of Tau Day 2011, this PEP proposes the addition of the circle
math.tau to the Python standard library.
The concept of
τ) is based on the observation that the ratio of a
circle’s circumference to its radius is far more fundamental and interesting
than the ratio between its circumference and diameter. It is simply a matter
of assigning a name to the value
2 * pi (
This PEP is now accepted and
math.tau will be a part of Python 3.6.
Happy birthday Alyssa!
The idea in this PEP has been implemented in the auspiciously named issue 12345.
The Rationale for Tau
pi is defined as the ratio of a circle’s circumference to its diameter.
However, a circle is defined by its centre point and its radius. This is
shown clearly when we note that the parameter of integration to go from a
circle’s circumference to its area is the radius, not the diameter. If we
use the diameter instead we have to divide by four to get rid of the
When working with radians, it is trivial to convert any given fraction of a
circle to a value in radians in terms of
tau. A quarter circle is
tau/4, a half circle is
tau/2, seven 25ths is
7*tau/25, etc. In
contrast with the equivalent expressions in terms of
14*pi/25), the unnecessary and needlessly confusing multiplication by
two is gone.
I’ve barely skimmed the surface of the many examples put forward to point out
just how much easier and more sensible many aspects of mathematics become
when conceived in terms of
tau rather than
pi. If you don’t find my
specific examples sufficiently persuasive, here are some more resources that
may be of interest:
- Michael Hartl is the primary instigator of Tau Day in his Tau Manifesto
- Bob Palais, the author of the original mathematics journal article
highlighting the problems with
pihas a page of resources on the topic
- For those that prefer videos to written text, Pi is wrong! and Pi is (still) wrong are available on YouTube
This document has been placed in the public domain.
Last modified: 2023-10-11 12:05:51 GMT