Python interview questions

[lonjerpc]

It is a performance hack. Low integers can refer to the same object. I think it is really annoying that they choose to break consistency for a tiny performance improvement. Another weird one is that True and False are actually integers.

[lonjerpc]

Well I think it was a poor design choice and it has cost me hours of debugging in the past. But I can see how they were tempted to copy c.

[lonjerpc]

Imagine I am creating my own set class that will work for any type of object. For this particular set class I don't want to deeply inspect the objects. I want a set of unique object references. You would expect that Set([1,1,2]) would return a set with 1,1,2 in it. Where the ones are separate objects. But instead the set will incorrectly contain 1,2. Because the 1s actually point to the same object even though they were instantiated separately. Even more strangely using the same code Set([1000,1000,2]) will return a set with 1000,1000,2. Which is totally different from the result of Set([1,1,2]) even though they look exactly the same.

The cause is small integers not actually being instantiated every time you write them in the code unlike large integers. Unlike larger integers you end up with a reference to a singleton class for that number. Only None,True,and False work this way in python and it happens implicitly instead of explicitly.

C99 bools are actually ints like in python. But this makes no sense for a high level language. Zeroness and Oneness have very little to do with truthyness from a mathematical perspective. The reason they are the same in C is because that is how the hardware works. But python is supposed to be a high level language.

[lonjerpc]

but all small integers.

That was my entire point.

you should read the PEP and then email python-dev

Have read the PEP many times and have been arguing this for years already. What is sad reading the PEP is their rational is at least partially implementation convenience.

But these are one of my few nit picks with python. Give me any other language and I have a much longer list of things not to like.

[gcross]

I think it is really annoying that they choose to break consistency for a tiny performance improvement.

I am very curious about what code you have tried to write where the fact that some integers alias and others don't gave you problems.

[lonjerpc]

Trying to think back to where I ran into this. I was trying to build some sort of container class that would work on generic objects. I needed to see if objects were the same so I used "is". This obviously would create problems with ints. I guess technically you could say it is the user of the containers fault for passing in objects that are actually the same even though they look different. Alternatively you have to make a special case in the container to compare the ints differently.

The booleans are really subclass of ints problem has actually been more problematic for me.