CODEWITHSUNDEEP
pythonlistcomparison
spl
spl

Reputation: 609

What happens when you compare lists of different sizes?

In Python, I have the two lists of different sizes:

x = [[0,5,10],[0,10,5]]
y = [100,500,900]

What is the comparison happening at each step when I run:

print x>y

e.g. How does it compare say the first element: [0,5,10] vs 100?

Upvotes: 0

Views: 103

Answers (5)

rmorshea
rmorshea

Reputation: 852

Essentially x == y uses the magic __eq__ method on objects to compare them. Different objects will behave differently, and you can even define your own custom equalities, but in general comparing objects of different types will always evaluate to False (Python2 and Python3 docs).

So in your example, [0,5,10] == 100 evaluates to False, not because it checked to see if the elements in the list were equal to 100, but because the two types were incompatible.

Upvotes: 0

RishiG
RishiG

Reputation: 2830

Just to expand on the other answers, the documentation is pretty good on this stuff. From the 2.7 documentation:

Sequence objects may be compared to other objects with the same sequence type. The comparison uses lexicographical ordering: first the first two items are compared, and if they differ this determines the outcome of the comparison; if they are equal, the next two items are compared, and so on, until either sequence is exhausted. If two items to be compared are themselves sequences of the same type, the lexicographical comparison is carried out recursively. If all items of two sequences compare equal, the sequences are considered equal.

From the 3.5 documentation:

Sequence objects may be compared to other objects with the same sequence type. The comparison uses lexicographical ordering: first the first two items are compared, and if they differ this determines the outcome of the comparison; if they are equal, the next two items are compared, and so on, until either sequence is exhausted. If two items to be compared are themselves sequences of the same type, the lexicographical comparison is carried out recursively. If all items of two sequences compare equal, the sequences are considered equal. If one sequence is an initial sub-sequence of the other, the shorter sequence is the smaller (lesser) one.

Upvotes: 0

Yu Hao
Yu Hao

Reputation: 122443

The real problem is how to compare [0,5,10] vs 100, i.e, a list vs an integer.

The answer depends on the Python version. In Python 3.x, the two types can't be compared. In Python 2.x, lists are always greater than integers because the type names list is greater than int.

In your example, the print statement in

print x>y

suggests that you are using Python 2.x, so the answer is x > y would be True.

Upvotes: 1

kindall
kindall

Reputation: 184260

In Python 3, you can't compare those two lists because their elements are not of comparable types.

In Python 2, lists are always greater than integers, period, so your x is always greater than your y regardless of what elements are in x's sublists.

Upvotes: 4

noteness
noteness

Reputation: 2520

Those comparisons won't work. list and int can't be compared. So it won't work

Upvotes: 0

Related Questions