CODEWITHSUNDEEP
pythonpython-2.7sorting
Shivkumar kondi
Shivkumar kondi

Reputation: 6782

How sorting occurs with different datatypes in python

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

Upvotes: 0

Views: 52

Answers (1)

Delgan
Delgan

Reputation: 19677

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.

Upvotes: 2

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