Yield solvers that fullfil the requirements.

def filter_solvers(solvers, requirements):
    """Yield solvers that fullfil the requirements."""
    for solver in solvers:
        for req, value in iteritems(requirements):
            if (req in ('integer', 'quadratic', 'rational', 'name') and
                    (req not in solver or solver[req] != value)):
                break
        else:
            yield solver