Sorting class instances in python

Question

What does python 2.7 use to sort vanilla class instances? I\'m interested in the default sorting behavior.

Suppose I have the class

class S():
    pa         


        

Answer 1

I tried your example on my own machine (python 2.7):

>>> sorted(l)
[(<__main__.S instance at 0x107142a70>, 'a'), (<__main__.S instance at 0x107142ab8>, 'b'), (<__main__.S instance at 0x107142b00>, 'c')]

Note that the sorted list is in order of the id():

>>> id(a)
4413729392
>>> id(b)
4413729464
>>> id(c)
4413729536

If I generate the hashes I get:

>>> hash(a)
275858087
>>> hash(b)
-9223372036578917717
>>> hash(c)
275858096

Which suggests that the sorting is not based on the hash.

See derekerdmann's answer for information on how to make python sort your class the way you want.

Edit: By the way, if you put the items in the list in reverse and then sort it, you get:

>>> l = [(c,'c'), (b, 'b'), (a, 'a')]
>>> sorted(l)
[(<__main__.S instance at 0x107142a70>, 'a'), (<__main__.S instance at 0x107142ab8>, 'b'), (<__main__.S instance at 0x107142b00>, 'c')]

Once again, its sorted in order of the id().