Why to use __setattr__ in python?

Question

I don\'t know for why using __setattr__ instead simple referencing like x.a=1.

I understand this example:

class Rectangle:         


        

Answer 1

the __setattr__ can be used to reflection, where an propperty on the object Rectangle can be created at runtime, there are more about it on http://en.wikipedia.org/wiki/Reflection_%28computer_science%29

class Rectangle:
    def __init__(self):
        #... code ...

x = Rectangle()
#x.__setattr__('newProperty',30)      Edited after comment
setattr(x, 'newProperty', 30)
print x.newProperty #>>> 30