Being already present in the numpy core libraries as NPY_EULER, this constant is not so easily accessible as pi or e, as one can not access it directly from vanilla numpy, but (presumably) from custom C-extensions only.
I'm plus +1 on this.
OK, pick a name ;)
I think something in the line of euler_gamma will suffice.
ENH: Expose Euler-Mascheroni constant.
This closes issue gh-2753.
See PR #2779