  Let $T$ be a torus acting on $\CC^n$ in such a way that, for all $1\leq k\leq
n$, the induced action on the grassmannian $G(k,n)$ has only isolated fixed
points. This paper proposes a natural, elementary, explicit description of the
corresponding $T$-equivariant Schubert calculus. In a suitable natural basis of
the $T$-equivariant cohomology, seen as a module over the $T$-equivariant
cohomology of a point, it is formally the same as the ordinary cohomology of a
grassmann bundle. The main result, useful for computational purposes, is that
the $T$-equivariant cohomology of $G(k,n)$ can be realized as the quotient of a
ring generated by derivations on the exterior algebra of a free module of rank
$n$ over the $T$-equivariant cohomology of a point.
