strange behavior of __new__ in python -

while reading __new__, came across example on stackoverflow itself. working on example, modified code slightly. modified code follows:

class a1(object):     def __new__(cls):         print 'in new'     def __init__(self):         print 'in init'  = a1()  class a(object):     _dict = dict()      def __new__(cls):         if 'key' in a._dict:             print "exists"             return a._dict['key']         else:             print "new"             return super(a, cls).__new__(cls)      def __init__(self):         print "init"         a._dict['key'] = self         print ""  a1 = a() a2 = a() a3 = a() 

the output follows:

in new new init  exists init  exists init 

that is, when instance created class 'a1', __new__ executed, whereas class 'a' instances both __new__ , __init__ being executed.

i not able figure out reason this.

you did not return new instance in first example; need return instance __init__ called on.

the following calls both __new__ , __init__ methods:

class a1(object) :     def __new__(cls) :         print 'in new'         return super(a1, cls).__new__(cls)      def __init__(self) :         print 'in init' 

demo:

>>> class a1(object) : ...     def __new__(cls) : ...         print 'in new' ...         return super(a1, cls).__new__(cls) ...     def __init__(self) : ...         print 'in init' ...  >>> a1() in new in init <__main__.a1 object @ 0x106e5d090>