Nearly matcher for floats

[mithrandi]

This would basically be for matching on floats when precision isn't controlled, although theoretically it'll work on any type that implements subtraction and abs():

class Nearly(object):
    """Within a certain threshold."""
    def __init__(self, expected, epsilon=0.001):
        self.expected = expected
        self.epsilon = epsilon

    def __str__(self):
        return 'Nearly(%r, %r)' % (self.expected, self.epsilon)

    def match(self, value):
        if abs(value - self.expected) > self.epsilon:
            return Mismatch(
                u'%r more than %r from %r' % (
                    value, self.epsilon, self.expected))