On 21/06/2013 19:26, Rick Johnson wrote:
On Friday, June 21, 2013 12:47:56 PM UTC-5, Rotwang wrote:
It isn't clear to me from your posts what exactly you're
proposing as an alternative to the way Python's default
argument binding works. In your version of Python, what
exactly would happen when I passed a mutable argument as a
default value in a def statement? E.g. this:
>>> a = [1, 2, 3]
>>> a.append(a)
>>> b = object()
>>> def f(x = [None, b, [a, [4]]]):
... pass # do something
What would you like to see the interpreter do in this case?
Ignoring that this is a completely contrived example that has
no use in the real world, here are one of three methods by
which i can handle this:
============================================================
The Benevolent Approach:
============================================================
I could cast a "virtual net" over my poor lemmings before
they jump off the cliff by throwing an exception:
Traceback (most recent screw-up last):
Line BLAH in SCRIPT
def f(x = [None, b, [a, [4]]]):
ArgumentError: No mutable default arguments allowed!
What about this:
def f(x=Foo()):
pass # do something
Should it raise an exception? Only if a Foo instance is mutable? How do
you know whether such an instance is mutable?
============================================================
The Apathetic Approach:
============================================================
I could just assume that a programmer is responsible for the
code he writes. If he passes mutables into a function as
default arguments, and then mutates the mutable later, too
bad, he'll understand the value of writing solid code after
a few trips to exception Hell.
============================================================
The Malevolent Approach (disguised as beneva-loon-icy):
============================================================
I could use early binding to confuse the hell out of him and
enjoy the laughs with all my ivory tower buddies as he falls
into fits of confusion and rage. Then enjoy again when he
reads the docs. Ahh, the gift that just keeps on giving!
How does the "Apathetic Approach" differ from the "Malevolent Approach"?
============================================================
Conclusion:
============================================================
As you can probably guess the malevolent approach has some
nice fringe benefits.
You know, out of all these post, not one of you guys has
presented a valid use-case that will give validity to the
existence of this PyWart -- at least not one that CANNOT be
reproduced by using my fine examples. All you can muster is
some weak argument about protecting the lemmings.
Is anyone up the challenge?
Does anyone here have any real chops?
PS: I won't be holding my breath.
Speaking of which, on 11 January 2013, in the thread "PyWart: Import
resolution order", you were asked:
"""Got any demonstrable code for Python 4000 yet?"""
and you said:
"""I am working on it. Stay tuned. Rick is going to rock your little
programming world /very/ soon."""
How soon is "/very/ soon" (clearly longer than 5 months), and how did
you fix this "PyWart"?
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