python - Implement classes Square and Triangle as subclasses of class Polygon -

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it overload constructor method init takes 1 argument(side length) , override method area computes area. came program, keeps saying "undefined name polygon".

class square(polygon):     'square class'      def __init__(self, s):         'constructor initializes side length of square'         polygon.__init__(self, 4, s)      def area(self):         'returns square area'         return self.s**2  math import sqrt class triangle(polygon):     def __init__(self, s):         'constructor initializes side length of equilateral triangle'         polygon.__init__(self, 3, s)      def area(self):         'returns triangle area'         return sqrt(3)*self.s**2/4

if want inherit polygon, have define before define other classes inherit it.

class polygon:     def __init__(self):         pass     def area(self):         raise notimplemented  class square(polygon):     'square class'      def __init__(self, s):         'constructor initializes side length of square'         polygon.__init__(self, 4, s)      def area(self):         'returns square area'         return self.s**2  math import sqrt class triangle(polygon):     def __init__(self, s):         'constructor initializes side length of equilateral triangle'         polygon.__init__(self, 3, s)      def area(self):         'returns triangle area'         return sqrt(3)*self.s**2/4

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