Python - User-defined classes have __cmp__() and __hash__() methods by default? Or?
comparison, default, methods, python
Solution
The documentation is a bit misleading. To get the full story, you have to read up on `__cmp__`, namely this part:
If no `__cmp__()`, `__eq__()` or `__ne__()` operation is defined, class instances are compared by object identity (“address”).
So, basically, you don't get a `__cmp__` method by default, but instances of user-defined classes can be compared to other objects; if the instance has no `__cmp__` method, the object identity (determined by `id(obj)`, which is usually the memory address of the object) will be used instead.
Problem
In the python docs (yeah, I have this thing with the docs) it says that: User-defined classes have `__cmp__()` and `__hash__()` methods by default; with them, all objects compare unequal (except with themselves) and `x.__hash__()` returns `id(x)`. But the following code shows another thing: ``` >>> class Test(object): pass ... >>> t = Test() >>> >>> t.__hash__ <method-wrapper '__hash__' of Test object at 0x01F2B5D0> >>> >>> t.__cmp__ Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'Test' object has no attribute '__cmp__' >>> ``` So where is `__cmp__` or what am I missing?