Issue #12345: Add mathemathcal constant tau to math and cmath.

Patch by Lisa Roach. See also PEP 628.

2 files changed, 11 insertions, 2 deletions

diff --git a/Doc/library/cmath.rst b/Doc/library/cmath.rst
index 62ddb6b..f04f8d0 100644
--- a/Doc/library/cmath.rst
+++ b/Doc/library/cmath.rst
@@ -253,6 +253,10 @@ Constants
 
    The mathematical constant *e*, as a float.
 
+.. data:: tau
+
+   The mathematical constant *τ*, as a float.
+
 .. index:: module: math
 
 Note that the selection of functions is similar, but not identical, to that in
@@ -276,5 +280,3 @@ cuts for numerical purposes, a good reference should be the following:
    Kahan, W:  Branch cuts for complex elementary functions; or, Much ado about
    nothing's sign bit.  In Iserles, A., and Powell, M. (eds.), The state of the art
    in numerical analysis. Clarendon Press (1987) pp165-211.
-
-
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index 3fdea18..32e1352 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -426,6 +426,13 @@ Constants
 
    The mathematical constant e = 2.718281..., to available precision.
 
+.. data:: tau
+
+   The mathematical constant τ = 6.283185..., to available precision.
+   Tau is a circle constant equal to 2π, the ratio of a circle's circumference to
+   its radius. To learn more about Tau, check out Vi Hart's video `Pi is (still)
+   Wrong <https://www.youtube.com/watch?v=jG7vhMMXagQ>`_, and start celebrating
+   `Tau day <http://tauday.com/>`_ by eating twice as much pie!
 
 .. data:: inf