How sorting occurs with different datatypes in python

Question

I have a custom list like this :

mylist1= [-2,0,1,1.5,2,3,6,8,5,'a','-%3','A',True,False,list(),tuple(),dict()]

Here I have most of the datatypes in this list,so I just tried to sort them and see how it sorts all them.

And It gave me output like this:

print sorted(mylist1)
[-2, 0, False, 1, True, 1.5, 2, 3, 5, 6, 8, {}, [], '-%3', 'A', 'a', ()]

Here we can see {} is placed before [] and () at the most end.

All I searched and got __cmp__ is running inside this mergesort. More info

I have two questions:

Question1:

I just want to know how this precedence of values with the different datatypes is defined in python

Question2:

If I include set() in above mylist, it won't run this sort. why so? it is showing TypeError: can only compare to a set

Why Down Vote?? I have asked a valid question after searching many things. If you know the answers please post it instead of downvoting — Shivkumar kondi
– Shivkumar kondi, Commented Mar 25, 2017 at 9:17
Don't ask multiple questions at once. And if you research, you find existing answers, e.g. stackoverflow.com/questions/3270680/… and 2, stackoverflow.com/questions/4084243/… — jonrsharpe
– jonrsharpe, Commented Mar 25, 2017 at 9:18
@jonrsharpe Thanks, but this were related questions of same list , so I asked. — Shivkumar kondi
– Shivkumar kondi, Commented Mar 25, 2017 at 9:21
I'm not sure what you're trying to say. Both of your questions are answered elsewhere; the second in particular is easy to find answers for, as you have an error message to search for. That's not a good reason to ask again. — jonrsharpe
– jonrsharpe, Commented Mar 25, 2017 at 9:28

Delgan · Accepted Answer · 2017-03-25 09:23:58Z

According to the Python2.7 tutorial:

Note that comparing objects of different types is legal. The outcome is deterministic but arbitrary: the types are ordered by their name. Thus, a list is always smaller than a string, a string is always smaller than a tuple, etc. Mixed numeric types are compared according to their numeric value, so 0 equals 0.0, etc.

Sets are only comparable between each others, so < can be used to compare super/sub-sets:

In addition, both Set and ImmutableSet support set to set comparisons. Two sets are equal if and only if every element of each set is contained in the other (each is a subset of the other). A set is less than another set if and only if the first set is a proper subset of the second set (is a subset, but is not equal). A set is greater than another set if and only if the first set is a proper superset of the second set (is a superset, but is not equal).

All these inconsistency explain why you should use Python 3 instead of Python 2.

Using Python 3, only compatible types are comparable.

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