Re: how to test for atomicity/mutability/hashability?
On Thu, Oct 7, 2010 at 12:13 PM, kj no.em...@please.post wrote: snip It would facilitate the implementation of t() to have a simple test for mutability. Is there one? Non-default hashability is an approximate heuristic: def is_immutable(x): try: hash(x) except TypeError: return False else: klass = type(x) return klass is object or klass.__hash__ is not object.__hash__ Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: how to test for atomicity/mutability/hashability?
kj no.em...@please.post writes: I want to implement a test t() that will return True if its two arguments are completely different. By this I mean that they don't share any non-atomic component. E.g., if a = [0, 1] b = [0, 1] c = [2, 3] d = [2, 3] A = (a, c, 0) B = (a, d, 1) C = (b, d, 0) The desired test t() would yield: t(A, B) - False (A and B share the mutable component a) t(A, C) - True (a =!= c, b =!= d, and 0 is not mutable) t(B, C) - False (B and C share the mutable component d) (=!= is shorthand with is not identical to.) It would facilitate the implementation of t() to have a simple test for mutability. Is there one? Thanks! ~kj I think defining mutability is subject to opinion, but here is a first approximation. def mutable(obj): return obj.__hash__ is None or type(obj).__hash__ == object.__hash__ def t(l1, l2): return not any(mutable(x) and x is y for x, y in zip(l1, l2)) a = [0, 1] b = [0, 1] c = [2, 3] d = [2, 3] A = (a, c, 0) B = (a, d, 1) C = (b, d, 0) t(A, B) False t(A, C) True t(B, C) False -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
Re: how to test for atomicity/mutability/hashability?
On Thu, Oct 7, 2010 at 1:46 PM, Arnaud Delobelle arno...@gmail.com wrote: kj no.em...@please.post writes: I want to implement a test t() that will return True if its two arguments are completely different. By this I mean that they don't share any non-atomic component. E.g., if a = [0, 1] b = [0, 1] c = [2, 3] d = [2, 3] A = (a, c, 0) B = (a, d, 1) C = (b, d, 0) The desired test t() would yield: t(A, B) - False (A and B share the mutable component a) t(A, C) - True (a =!= c, b =!= d, and 0 is not mutable) t(B, C) - False (B and C share the mutable component d) (=!= is shorthand with is not identical to.) It would facilitate the implementation of t() to have a simple test for mutability. Is there one? Thanks! ~kj I think defining mutability is subject to opinion, but here is a first approximation. def mutable(obj): return obj.__hash__ is None or type(obj).__hash__ == object.__hash__ Corner case (I think): a = object() a.b = c Traceback (most recent call last): File stdin, line 1, in module AttributeError: 'object' object has no attribute 'b' mutable(a) True Cheers, Chris -- http://mail.python.org/mailman/listinfo/python-list
Re: how to test for atomicity/mutability/hashability?
Chris Rebert c...@rebertia.com writes: On Thu, Oct 7, 2010 at 1:46 PM, Arnaud Delobelle arno...@gmail.com wrote: [...] I think defining mutability is subject to opinion, but here is a first approximation. def mutable(obj): return obj.__hash__ is None or type(obj).__hash__ == object.__hash__ Corner case (I think): a = object() a.b = c Traceback (most recent call last): File stdin, line 1, in module AttributeError: 'object' object has no attribute 'b' mutable(a) True Ah true. There was also the problem that e.g. mutable(tuple) was False. How about this second approximation: def mutable(obj): h = type(obj).__hash__ return not h or h is object.__hash__ and type(obj) is not object -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
Re: how to test for atomicity/mutability/hashability?
Am 07.10.2010 22:02, schrieb Chris Rebert:
On Thu, Oct 7, 2010 at 12:13 PM, kj no.em...@please.post wrote:
snip
It would facilitate the implementation of t() to have a simple test
for mutability. Is there one?
Non-default hashability is an approximate heuristic:
Except that every user defined class is hashable and mutable by default ;)
class Example(object):
... pass
...
example = Example()
hash(example)
139810551284624
example.__dict__
{}
example.egg = spam
example.__dict__
{'egg': 'spam'}
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Re: how to test for atomicity/mutability/hashability?
On Thu, Oct 7, 2010 at 2:28 PM, Christian Heimes li...@cheimes.de wrote:
Am 07.10.2010 22:02, schrieb Chris Rebert:
On Thu, Oct 7, 2010 at 12:13 PM, kj no.em...@please.post wrote:
snip
It would facilitate the implementation of t() to have a simple test
for mutability. Is there one?
Non-default hashability is an approximate heuristic:
Except that every user defined class is hashable and mutable by default ;)
class Example(object):
... pass
...
example = Example()
hash(example)
139810551284624
example.__dict__
{}
example.egg = spam
example.__dict__
{'egg': 'spam'}
Hence exactly why I said *non-default* hashability (i.e. the object is
hashable, but does not use the default implementation which you point
out exists):
is_immutable(Example())
False
Not that the heuristic I suggested is infallible or anything though.
Cheers,
Chris
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