class Square:
    def __init__(self, L):
        self._L = L # note the underscore 
        A = self.area
        if A > 10.0:
            raise ValueError(f'Area {A} above limit 10.0')

    # getter, defines self.L 
    @property
    def L(self):
        return self._L
        
    @property
    def area(self):
        return self.L**2

if __name__=='__main__':
    small_sq = Square(0.5)    
    print(f'small square: L = { small_sq.L} area = {small_sq.area}')
    
    # you are not allowed to change L after init     
    small_sq.L = 10.0 # raises AttributeError
    # you are not allowed to define squares with area > 10.0
    big_sq = Square(50.0) # raises ValueError
    print(f'  big square: L = { big_sq.L} area = {big_sq.area}')