[Python-ideas] Fwd: Define a method or function attributeoutsideof a class with the dot operator
steve at pearwood.info
Mon Feb 13 19:44:14 EST 2017
On Mon, Feb 13, 2017 at 11:50:09AM -0800, Matt Gilson wrote:
> For whatever weight my opinion holds, I'm +0 on this one. In my
> estimation, in an ideal world it seems like:
> class Foo(object):
> def bar(self):
> # Identical to:
> class Foo(object): pass
> def Foo.bar(self):
> But I think that's going to be hard to achieve given implicit binding of
> `super` (as some have already mentioned) and more mind-bendingly when
> user-defined metaclasses are in play.
I think that this is too high a bar to reach (pun not intended). A
metaclass can do anything it likes to the methods in the class, and
injecting a method after the class already exists is not necessarily the
same as including it in the initial namespace argument passed to the
I think a more reasonable bar is to have
def Foo.bar(self): ...
def bar(self): ...
Foo.bar = bar # Foo is a class
except that the usual class magic like setting __qualname__, super()
etc will work. That feels doable.
For instances, the invariant should be slightly different:
def bar(self): ...
foo.bar = types.MethodType(bar, foo) # foo is an instance
> Indeed, with metaclasses, it seems
> like it become impossible to actually guarantee the equality of the above
> two blocks of code. Maybe the PEP writers are OK with that, but that
> should be decided at the outset...
> Also note that if users start adopting this as their default mode of class
> creation (rather than just *class extending*), code-folding in a lot of
> IDEs won't handle it gracefully (at least not for quite a while).
Why would people use this as the default mode of class creation?
I mean, sure there's always that *one guy* who insists on their own
weird idiosyncratic way of doing things. I know somebody who refuses to
use for loops, and writes all his loops using while. But I can't see
this becoming a widespread practice. We all have our quirks, but most of
our quirks are not that quirky.
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