在同一模块中定义类型时使用类型提示

Question

我正在尝试使用类型提示（Python中的新功能）来使代码更具可读性：

class Point:

    def __init__(self, x: float, y:float):
        self.x = x
        self.y = y

    def is_in_rectangle(self, rectangle: Rectangle):
        if rectangle.lower_left.x < self.x < rectangle.upper_right.x \
        and rectangle.lower_left.y < self.y < rectangle.upper_right.y:
            return True
        else:
            return False

class Rectangle:

    def __init__(self, lower_left: Point, upper_right: Point):
        self.lower_left = lower_left
        self.upper_right = upper_right

执行该代码时，我得到：

NameError                                 Traceback (most recent call last)
<ipython-input-1-c01b4ce97fcf> in <module>
----> 1 class Point:
      2 
      3     def __init__(self, x: float, y:float):
      4         self.x = x
      5         self.y = y

<ipython-input-1-c01b4ce97fcf> in Point()
      5         self.y = y
      6 
----> 7     def is_in_rectangle(self, rectangle: Rectangle):
      8         if rectangle.lower_left.x < self.x < rectangle.upper_right.x \
      9         and rectangle.lower_left.y < self.y < rectangle.upper_right.y:

NameError: name 'Rectangle' is not defined

我该如何解决？

如果我在Point上定义Rectangle，那么我会得到一个NameError: name 'Point' is not defined。