'Create a new :class:`.hybrid_method`.
Usage is typically via decorator::
from sqlalchemy.ext.hybrid import hybrid_method
class SomeClass(object):
@hybrid_method
def value(self, x, y):
return self._value + x + y
@value.expression
def value(self, x, y):
return func.some_function(self._value, x, y)'

def __init__(self, func, expr=None):

    self.func = func
    self.expr = (expr or func)
