Re: Hashable object with self references OR how to create a tuple that refers to itself
Dieter Maurer die...@handshake.de wrote: You can create a tuple in C and then put a reference to itself into it, but I am quite convinced that you cannot do it in Python itself. (Of course, you could use cython to generate C code with a source language very similar to Python). I don't think you can even do it in C without breaking the specified API: PyTuple_SetItem fails if the reference count of the tuple is not 1, but it also steals the reference of the object that is being added to the tuple so if you don't increment the reference count before attempting to add the tuple to itself you've broken the rules for reference counting. -- Duncan Booth http://kupuguy.blogspot.com -- http://mail.python.org/mailman/listinfo/python-list
Hashable object with self references OR how to create a tuple that refers to itself
I am trying to create a collection of hashable objects, where each object contains references to other objects in the collection. The references may be circular. To simplify, one can define x= list() x.append(x) which satisfies x == [x]. Can I create a similar object for tuples which satisfies x == (x,)? -- http://mail.python.org/mailman/listinfo/python-list
Re: Hashable object with self references OR how to create a tuple that refers to itself
Edward C. Jones edcjo...@comcast.net writes:
I am trying to create a collection of hashable objects, where each
object contains references to
other objects in the collection. The references may be circular.
To simplify, one can define
x= list()
x.append(x)
which satisfies x == [x].
Can I create a similar object for tuples which satisfies x == (x,)?
You can create a tuple in C and then put a reference to itself into it,
but I am quite convinced that you cannot do it in Python itself.
(Of course, you could use cython to generate C code with a source language
very similar to Python).
But, you do not need tuples; You could use a standard class:
class C(object): pass
...
c=C()
c.c=c
d=dict(c=c)
d
{'c': __main__.C object at 0xb737f86c}
--
Dieter
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http://mail.python.org/mailman/listinfo/python-list
RE: Hashable object with self references OR how to create a tuple that refers to itself
I am trying to create a collection of hashable objects, where each
object contains references to
other objects in the collection. The references may be circular.
To simplify, one can define
x= list()
x.append(x)
which satisfies x == [x].
Can I create a similar object for tuples which satisfies x == (x,)?
You can create a tuple in C and then put a reference to itself into it,
but I am quite convinced that you cannot do it in Python itself.
(Of course, you could use cython to generate C code with a source
language
very similar to Python).
But, you do not need tuples; You could use a standard class:
class C(object): pass
...
c=C()
c.c=c
d=dict(c=c)
d
{'c': __main__.C object at 0xb737f86c}
Using a class is a good approach. You can also override __contains__
for the custom classes internal collection so instead of x==[x,] you
would use x in obj where obj is a collection with the equivalent [x,].
Not entirely sure why Dieter is bringing up C code / Cython...
Just as a note, if you store references to an object A in the collection
in another object B in the collection and then try to remove A from the
collection it will not get garbage collected nor removed from B. To
allow for garbage collection you should store a weakref instead.
http://docs.python.org/library/weakref.html
Ramit
Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
712 Main Street | Houston, TX 77002
work phone: 713 - 216 - 5423
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