🔒 dunder method questions

[timber tartan]

@azure ibex

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[peak zodiac]

Think about Number(5) + Number(5) + Number(5) actually become
Number(5).__add__(Number(5)).__add__(Number(5))

So when you compute Number(5).__add__(Number(5)) and get the equivalent of Number(10), it essentially becomes Number(10).__add__(Number(5)

Basically syntax sugar kind of thing

2. Eventually it go to level of C++ code which handled it

[abstract timber]

There's no "triggering another one" in the int class

[peak zodiac]

In this case, int

int is written in C++, not python

[abstract timber]

Which in turn uses a binary algorithm to add ints

[abstract timber]

Well, C

CPython, not CppPython hah

the official Python interpreter is written in C

all the builtin types are written in C

it's a python object still, just at the C level

[craggy marlin]

why would the __add__ in int cause Number.__add__ to be triggered?

damn, I didn't see the history

anyways, instead of TypeError you should just return NotImplemented

this lets the other operand implement its own __add__

[abstract timber]

(Well, __radd__?)

[peak zodiac]

That was to increase priority of the reverse first I think

Even if it works without reversing

[abstract timber]

!e

class A:
    def __add__(self, other):
        print("add first")

class B:
    def __radd__(self, other):
        print("radd first")

A() + B()

[timber tartan]

:white_check_mark: Your 3.13 eval job has completed with return code 0.

add first

[abstract timber]

nope

[peak zodiac]

Hmm

[abstract timber]

it goes like this

1. try to call __dunder__ on the LHS
2. if that fails, try to call __rdunder__ on the RHS

!e therefore, this errors

class A: ...

class B:
    def __add__(self, other):
        print("add")

A() + B()

[timber tartan]

:x: Your 3.13 eval job has completed with return code 1.

001 | Traceback (most recent call last):
002 |   File "/home/main.py", line 7, in <module>
003 |     A() + B()
004 |     ~~~~^~~~~
005 | TypeError: unsupported operand type(s) for +: 'A' and 'B'

[peak zodiac]

Hmm ok

[abstract timber]

part of the reason is that you can't assume the operator is commutative for the given operands

for example, string concatenation is not commutative

[timber tartan]

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