The aliases module contains a set of matcher aliases that are most commonly used when composing matchers and are not meant to be imported every time.
To use the aliases just import them:
from expects import *
from expects.aliases import *
expect([1, 2]).to(contain_exactly(an(int), 2))
The same code without using the an alias for the be_an matcher:
from expects import *
expect([1, 2]).to(contain_exactly(be_an(int), 2))