props.md

Why are only the properties defined in __init__ listed in the __dict__ attribute of an instance of the class?

Python 3.4.3 (default, Jan 11 2016, 09:37:52)
[GCC 4.9.3] on linux
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>>> class C(object):
...     prop_1 = 'value 1'
...     def __init__(self):
...         self.prop_2 = 'value 2'
...     def set_prop_3(self):
...         return 'value 3'
...     prop_3 = property(set_prop_3)
...
>>> C.__dict__
mappingproxy({'__doc__': None, '__weakref__': <attribute '__weakref__' of 'C' objects>, '__dict__': <attribute '__dict__' of 'C' objects>, 'prop_3': <property object at 0x7f62a1817598>, '__init__': <function C.__init__ at 0x7f62a1813840>, 'prop_1': 'value 1', '__module__': '__main__', 'set_prop_3': <function C.set_prop_3 at 0x7f62a18138c8>})
>>> C().__dict__
{'prop_2': 'value 2'}
>>>