On Fri, Mar 01, 2019 at 08:59:45PM +0900, INADA Naoki wrote:
> I dislike adding more operator overload to builtin types.
>
> str is not commutative, but it satisfies a in (a+b), and b in (a+b).
> There are no loss.
Is this an invariant you expect to apply for other classes that support
the addition operator?
5 in (5 + 6)
[1, 2, 3] in ([1, 2, 3] + [4, 5, 6])
Since it doesn't apply for int, float, complex, list or tuple, why do
you think it must apply to dicts?
> In case of dict + dict, it not only sum. There may be loss value.
Yes? Why is that a problem?
> {"a":1} + {"a":2} = ?
Would you like to argue that Counter.__add__ is a mistake for the same
reason?
Counter(('a', 1)) + Counter(('a', 2)) = ?
For the record, what I expected the above to do turned out to be
*completely wrong* when I tried it. I expected Counter({'a': 3}) but the
actual results are Counter({'a': 2, 1: 1, 2: 1}).
Every operation is going to be mysterious if you have never
learned what it does:
from array import array
a = array('i', [1, 2, 3])
b = array('i', [10, 20, 30])
a + b = ?
Without trying it or reading the docs, should that be an
error, or concatenation, or element-wise addition?
> In case of a.update(b), it's clear that b wins.
It wasn't clear to me when I was a beginner and first came across
dict.update. I had to learn what it did by experimenting with manual
loops until it made sense to me.
> In case of a + b, "which wins" or "exception raised on duplicated key?" is
> unclear to me.
Many things are unclear to me too. That doesn't make them any less
useful.
--
Steven
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