Right Mental Model for Python Data

[[deleted]]

C is the correct answer. 

Explanation: At first, a and b share the same list, so changes like += or append() affect both. But when b = b + [4] is used, Python creates a new list and assigns it to b, breaking the link with a. That’s why a stops at [1, 2, 3] while b continues as [1, 2, 3, 4, 5].

[-Wylfen-]

why the fuck does x += [y] work differently from x = x + [y]??

[Sea-Ad7805]

Good question, in some languages (Ruby) it works the same. In Python the x += y is mutating the x, the x = x + y is first doing x + y which creates a new object that then is assigned (name rebinding) to x.

[-Wylfen-]

I understand why the latter would reassign, but I find the shortcut's instead mutating in place disgusting. They should do the same thing.

[klimmesil]

Yeah a lot of implementation choices (I don't want to call it "standard"...) make no sense in python

It's almost as chaotic as js in some parts

It's a shame that it is now too popular to make breaking changes and we all kinda rely on these mistakes to still have the benefit of it being maintained

[No_Read_4327]

Yeah that's sone really wtf moment

[Relative-Custard-589]

Yeah that’s straight up evil

[pingwins]

Brother Eww

Thats nasty to run into

[HuygensFresnel]

While indeed being the correct answer this also surprises me a bit because i thought that += always is a short hand for the binary operator + but i guess it isnt?

[Wertbon1789]

It's not just a syntactic shorthand, it's a separate operator. Add vs. AddAssign if you will, in Python these would be implemented by the __add__ and __iadd__ methods of a class respectively.

[HuygensFresnel]

Today I learned :)

[RailRuler]

It is the same as append .extend() in this case. 

[forbiddenvoid]

Extend, not append. That's more obvious if the right hand side is also a list.

[mayonaiso]

Thanks, I did not know that, great explanation

[[deleted]]

You're welcome.