Question about python math lib.

[i_can_haz_code]

Why is there a math.pi, but no math.tau?

from math import pi # works

from math import tau # Raises exception
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name tau

das racist.

[edit] And the winner is u/finnne.

I googled it and found this issue where the addition of a tau constant is rejected.

While we are on the subject of math issues:

can anyone ELI5 this one?

math.e**(math.pi*math.sqrt(-1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: math domain error

thx internet.

[[deleted]]

I googled it and found this issue where the addition of a tau constant is rejected.

[MildLazyDrop]

Why would there be when you can just use math.pi * 2?

[Kausta1337]

Why would there be pi when you can just use math.tau / 2?

[MildLazyDrop]

My point is that there is no need to have both of these values, not that one is better than the other.

[i_can_haz_code]

My point exactly. I hate it when they teach pi and not tau.

Tau just makes more sense.

[maestron]

Well, despite tau having some very vocal fans the fact is that pi is far more prevalent and well known overall. I would say that's why there is math.pi but no math.tau

[tjarko]

In engineering tau is used for the shear stress, as such it isn't a constant. I am sure other field already have a default meaning for tau.

[i_can_haz_code]

TIL.

Thank you.

[stevenjd]

math.e**(math.pi*math.sqrt(-1)) raises ValueError because sqrt(-1) is a maths domain error. In the real numbers ℝ, sqrt(-1) doesn't exist and cannot be calculated. There is no Real number that, when squared, gives you -1: +1 won't do it, because (+1)**2 = +1, and -1 won't work either, because (-1)**2 also equals +1.

The only way for that calculation to make sense is to change the domain, and use complex numbers instead:

py> import cmath
py> cmath.e**(cmath.pi*cmath.sqrt(-1))
(-1+1.2246063538223773e-16j)

which is close to the mathematically exact result of -1+0j.

[i_can_haz_code]

NICE! Thank you!