Hard Python Dictionary Exercise (lemmy.nz)

submitted 2 weeks ago by bterwijn@programming.dev to c/python@programming.dev

35 comments fedilink hide all child comments

A hard exercise to help build the right mental model for Python data.

The “Solution” link visualizes execution and reveals what’s actually happening using 𝗺𝗲𝗺𝗼𝗿𝘆_𝗴𝗿𝗮𝗽𝗵: https://github.com/bterwijn/memory_graph

you are viewing a single comment's thread
view the rest of the comments

[-] bterwijn@programming.dev 3 points 2 weeks ago* (last edited 2 weeks ago)

I think the confusion comes from a += b being equivalent to a = a + b for immutable types, so some people generalize that incorrectly to mutable types too. Otherwise I think it's pretty clear a += b mutates a, and a = a + b first computes a + b and then reassigns that to a so that its identity changes, just like in c = a + b.

If you implement these operations in a class you have to implement each dunder, __iadd__(self, other) and __add__(self, other) separately, same thing in C++.

[-] sukhmel@programming.dev 1 points 2 weeks ago

It is only clear if you already have a model of how labels work in Python and while it is understandable to me now, I wouldn't say this is anything I would expect

Then again, shadowing variables is allowed in other languages and is also a source of confusion and mistakes at times

[-] bterwijn@programming.dev 1 points 2 weeks ago

The point of the visualization at the Solution link is precisely to help people get the right model of how labels and the data model in general works in Python. See the Explanation link for more details.