Python: cmp and str?

Question

What happens if you don't define your own for methods __cmp__ and __str__?

score 6 · Accepted Answer · edited May 23 '17 at 10:34

6

If no __cmp__(), __eq__() or __ne__() operation is defined, class instances are compared by object identity (“address”).

For more detailed info: refer to object.__cmp__(self, other) in Python. And you can get further references Special (magic) methods in Python.

edited May 23 '17 at 10:34

Community

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answered Apr 19 '12 at 05:22

Drake Guan

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score 6 · Answer 2 · answered Apr 19 '12 at 05:24

With no __str__ defined, you will get the default one with the memory address e.g. <__main__.A object at 0x165aa90>.

If no __cmp__() operation is defined, class instances are compared by object identity i.e. memory address (docs).

Examples:

>>> class A(object):
...   pass
... 
>>> a = A()
>>> b = A()
>>> str(a)
'<__main__.A object at 0x7fcb1df8acd0>'
>>> hex(id(a))
'0x7fcb1df8acd0'
>>> a < b
False
>>> a > b
True
>>> id(a), id(b)
(140510357925072, 140510357925008)

Python: __cmp__ and __str__?

2 Answers2

Python: cmp and str?