(An Unofficial) Python Reference Wiki

"clearly marked experimental"

5f3j

(effbot: fixed markup glitch)

Users trying this out should be aware that the latest 2.5 release, 2.5a2, implements a slightly different protocol whereby the guard object is obtained by calling the __context__() method on the expression in the with-statement. However, in most cases __context__() returns self, so the effect is the same (the decimal.Context class is the one exception). In Python 2.5a3 the __context__() method will be gone, and the above description will apply.