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

  • lad@programming.devEnglish
    3·
    18 hours ago

    I don’t think mutability is wrong as a concept, albeit I enjoyed learning and toying with Haskell, but I really think these functions in Python should have been two sets of operations, one set to do what a += b does and one set to do what a = a + b does.

    I’ve been doing C++ for quite some time and amount of implicit things that happen magically and not everyone get them right and this leads to bugs and confusion had really grown on me with time, and I feel like this is the same pattern here, where we get implicit magic instead of being clear with intentions and results

    • bterwijn@programming.devOP
      3·
      18 hours 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++.