Jan Greis wrote:
> On 22/10/2019 06:43, Richard Musil wrote:
> > It is not a "concatenation" though, because you lost
> > {"key1": "val1"}
> > in the process. The concatenation is not _just_ "writing something
> > after something", you can do it with anything, but the actual
> > operation, producing the result.
> > My point is that if I saw {"key1": "val1", "key2": "val2"} + {"key1":
> "val3"}, I would expect that it would be equivalent to {"key1": "val1",
> "key2": "val2", "key1": "val3"}.
But that reasoning only works with literals. And chances are that you're not
going to see something like this in real code. Because why would you add two
dict literals?
Instead you're going to see something like this: `d1 + d2`. And if one has to
infer the details of that operation by coming up with some hypothetical example
involving literals, that doesn't speak in favor of the syntax.
As mentioned, here it is up to the variable names to be clear about what
happens. E.g.
default_preferences + user_preferences
For that example it's pretty clear that `user_preferences` is meant to
supersede `default_preferences`. But variable names might not always be
completely clear or even if they are, they might not allow the reader to infer
any precedence. And then, "in the face of [that] ambiguity", one has to "refuse
the temptation to guess". Maybe it's better not to introduce that ambiguity in
the first place.
> Similarly, I would expect that
> deque([1, 2, 3], maxlen=4) + deque([4, 5]) == deque([1, 2, 3, 4, 5],
> maxlen=4) == deque([2, 3, 4, 5], maxlen=4)
> which indeed is true.
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