The series module implements series expansions as a function. This is achieved by creating a wrapper around Basic.series(). This allows for the use of series(x*cos(x),x), which is possibly more intuative than (x*cos(x)).series(x).
>>> from sympy import Symbol, cos, series >>> x = Symbol('x') >>> series(cos(x),x) 1 - x**2/2 + x**4/24 + O(x**6)
The series expansion about a point other than x=0 does not work. This is a bug in Basic.series() (issue 1334). When fixed there, the bug will also be automatically fixed here.