C Anthony Risinger writes:

 > I'm not versed enough in the math behind it to know if it's expected or
 > not, but as it stands, to remain compatible with sets, `d1 | d2` should
 > behave like it does in my code (prefer the first, not the last).  I kinda
 > like this, because it makes dict.__or__ a *companion* to .update(), not a
 > replacement (since update prefers the last).

But this is exactly the opposite of what the people who advocate use
of an operator want.  As far as I can see, all of them want update
semantics, because that's the more common use case where the current
idioms feel burdensome.