(1) hash()-ability != immutability (!)
Proof:
class X:
def __hash__(self): return 0
def pseudo_isimmutable(this):
try:
hash(this)
return True
except TypeError:
return False
shapeshifter = (1, 2, X())
print pseudo_isimmutable(shapeshifter)
On Tue, Nov 12, 2013 at 8:12 PM, Frank-Rene Schäfer fsch...@gmail.com wrote:
(1) hash()-ability != immutability (!)
Proof:
class X:
def __hash__(self): return 0
x == y != y == x
Proof:
class X:
def __eq__(self,other): return True
class Y:
def __eq__(self,other): return False
All you've done is proven that you can subvert things. By fiddling
with __hash__, __eq__, and so on, you can make sets and dicts behave
very oddly. Means nothing.
To the contrary, it means everything about what 'isimmutable' could
contribute: security against advert or inadvert insertion of
On Tue, Nov 12, 2013 at 8:39 PM, Frank-Rene Schäfer fsch...@gmail.com wrote:
All you've done is proven that you can subvert things. By fiddling
with __hash__, __eq__, and so on, you can make sets and dicts behave
very oddly. Means nothing.
To the contrary, it means everything about what
So how do you figure out whether something's immutable or not? Are you
going to ask the object itself? If so, stick with __hash__, and just
follow the rule that mutable objects aren't hashable - which is, if
I'm not mistaken, how things already are. And if not, then how? How
will you know if
On Tue, 12 Nov 2013 18:12:43 +1100, Chris Angelico wrote:
def isimmutable(x):
try:
hash(x)
return True
except TypeError:
return False
I'm afraid that doesn't test for immutability. It tests for hashability,
which is different.
No well-behaved mutable
On Tue, 12 Nov 2013 08:01:19 +0100, Frank-Rene Schäfer wrote:
the existence of a built-in function 'isimmutable' puts the concept of
immutability some more into the spotlight.
That is an argument against the proposal, not in favour. The concept of
immutability doesn't need to be in the
On 2013-11-12 11:14, Steven D'Aprano wrote:
On Tue, 12 Nov 2013 18:12:43 +1100, Chris Angelico wrote:
def isimmutable(x):
try:
hash(x)
return True
except TypeError:
return False
I'm afraid that doesn't test for immutability. It tests for hashability,
=?UTF-8?Q?Frank=2DRene_Sch=C3=A4fer?= fsch...@gmail.com wrote:
The ImmutableNester special class type would be a feature to help
checks to avoid recursion. Objects of classes derived from
ImmutableNester have no mutable access functions and allow insertion
of members only at construction
On Tue, Nov 12, 2013, at 4:39, Frank-Rene Schäfer wrote:
All you've done is proven that you can subvert things. By fiddling
with __hash__, __eq__, and so on, you can make sets and dicts behave
very oddly. Means nothing.
To the contrary, it means everything about what 'isimmutable' could
On 12/11/2013 11:10, Frank-Rene Schäfer wrote:
Admittedly, I have no knowledge about the python implementation.
There is no the regarding Python implementations. Cpython alone is at
either 2.7.6 or 3.3.3 with 3.4 at alpha, then there's IronPython,
Jython, PyPy and lots more that I'm sure
I prepared a PEP and was wondering what your thoughts are about it:
PEP:pep number
Title: ``isimmutable(Obj)`` and/or ``ImmutableNester``
Version:version string
Last-Modified: date string
Author: Frank-Rene Schaefer, fsch...@users.sourceforge.net
*
On Monday, November 11, 2013 3:47:45 PM UTC-5, Frank-Rene Schäfer wrote:
I prepared a PEP and was wondering what your thoughts are about it:
The best place to discuss proposals for changes to the Python language and
library is the Python-Ideas mailing list:
A built-in function 'isimmutable()' shall tell efficiently whether the
object
of concern is mutable or not.
What's the benefit over attempting to hash() the object?
copy.deepcopy already has special case for int, string, and tuples
(including tuples that do and do not have mutable members) -
On Mon, 11 Nov 2013 12:55:56 -0800, Ned Batchelder wrote:
On Monday, November 11, 2013 3:47:45 PM UTC-5, Frank-Rene Schäfer wrote:
I prepared a PEP and was wondering what your thoughts are about it:
The best place to discuss proposals for changes to the Python language
and library is the
On 12/11/2013 00:17, Steven D'Aprano wrote:
On Mon, 11 Nov 2013 12:55:56 -0800, Ned Batchelder wrote:
On Monday, November 11, 2013 3:47:45 PM UTC-5, Frank-Rene Schäfer wrote:
I prepared a PEP and was wondering what your thoughts are about it:
The best place to discuss proposals for changes
On Tue, Nov 12, 2013 at 11:17 AM, Steven D'Aprano
steve+comp.lang.pyt...@pearwood.info wrote:
On Mon, 11 Nov 2013 12:55:56 -0800, Ned Batchelder wrote:
On Monday, November 11, 2013 3:47:45 PM UTC-5, Frank-Rene Schäfer wrote:
I prepared a PEP and was wondering what your thoughts are about it:
Hi Frank-Rene, and welcome. Comments below.
On Mon, 11 Nov 2013 21:47:45 +0100, Frank-Rene Schäfer wrote:
I prepared a PEP and was wondering what your thoughts are about it:
PEP:pep number
Title: ``isimmutable(Obj)`` and/or ``ImmutableNester``
[...]
*
A tuple is immutable but it may contain mutable objects. In larger
hierarchies of objects it may become less obvious whether down
the lines, there is some mutable object somewhere in the data tree.
One can define a recursive function to check for immutability
manually. However first, it may not
On Tue, Nov 12, 2013 at 6:01 PM, Frank-Rene Schäfer fsch...@gmail.com wrote:
A tuple is immutable but it may contain mutable objects. In larger
hierarchies of objects it may become less obvious whether down
the lines, there is some mutable object somewhere in the data tree.
One can define a
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