Why does python chooses an empty list over empty dictionary and non-empty dictionary over non-empty list while using the "or" operator?

Question

I have been wondering about the use of or for choosing between two items if one has the probability of having the value of None, instead of using if else, (which I think is great btw)

Two examples:

None or [] -> returns []
None or {} -> returns {}

I've tried to use or in a scenario where one variable can be an empty dictionary and other can be an empty list. In this scenario the or returns the list but if the dictionary is non-empty, the dictionary is always chosen over the other variable. Results are the same i in both python 2.7.17 and python 3.6.9.

Examples:

{} or [] -> returns []
{1:2} or [2] -> returns {1:2}

Questions:

Is there a preference of an empty list over an empty dictionary?
Is there a preference of a non-empty dictionary over an non-empty list?
If there is no preference order, does any other rules/factors determines the outcome of this operation?

Thank you for your time and answers :) Have a good day.

The `or` operator returns the first truthy value from left to right. — Barmar, Feb 01 '21 at 20:01
Not exactly duplicate, but the answer can be found here, as well: https://stackoverflow.com/questions/16201362/in-which-order-is-an-if-statement-evaluated-in-python — quantumswing, Feb 01 '21 at 20:03
`{} or []` returns `[]`, `[] or {}` returns `{}`. See the pattern? — Barmar, Feb 01 '21 at 20:03
[Here](https://docs.python.org/3/library/stdtypes.html#boolean-operations-and-or-not) are the relevant docs — juanpa.arrivillaga, Feb 01 '21 at 20:04
Great I missed that, thanks. {} or [] -> returns [] because since the empty dict is False and the or operator assumes that the second one is True? — Mithun Kinarullathil, Feb 01 '21 at 20:05
It’s not that it “assumes it’s true”. If the first expression is falsey, it returns the second. If that’s *also* falsey, well, then the entire expression is falsey. — deceze, Feb 01 '21 at 20:07
Yes. This is called short circuiting. Evaluation of Boolean expressions from left to right is stopped when it is clear that the expression is true. If the entire expression is false, it proceeds to the end before it returns the final false value. Empty data structures have a false value. — pakpe, Feb 01 '21 at 20:11

Why does python chooses an empty list over empty dictionary and non-empty dictionary over non-empty list while using the "or" operator?

0 Answers0