object-identity

The following makes sense to me: >>> [] is [] False Given that lists are mutable, I would expect [] to be a new empty list object every time it appears in an expression. Using this explanation however, the following surprises me: id([]) == id([]) True Why? What is the explanation? In the first example, [] is not [] precisely because the lists are mutable. If they weren't, they could safely map to the same one without issue. In the second example, id([]) creates a list, gets the id, and deallocates the list. The second time around it creates a list again , but "puts it in the same place"

When the p function is used to print out an object, it may give an ID, and it is different from what object_id() gives. What is the reason for the different numbers? Update: 0x4684abc is different from 36971870 , which is 0x234255E >> a = Point.new => #<Point:0x4684abc> >> a.object_id => 36971870 >> a.__id__ => 36971870 >> "%X" % a.object_id => "234255E" Arkku The default implementation of inspect calls the default implementation of to_s , which just shows the hexadecimal value of the object directly, as seen in the Object#to_s docs (click on the method description to reveal the source).

I've started learning Python (python 3.3) and I was trying out the is operator. I tried this: >>> b = 'is it the space?' >>> a = 'is it the space?' >>> a is b False >>> c = 'isitthespace' >>> d = 'isitthespace' >>> c is d True >>> e = 'isitthespace?' >>> f = 'isitthespace?' >>> e is f False It seems like the space and the question mark make the is behave differently. What's going on? EDIT: I know I should be using == , I just wanted to know why is behaves like this. Elazar Warning: this answer is about the implementation details of a specific python interpreter. comparing strings with is ==bad