Feature Requests item #1297986, was opened at 2005-09-21 12:55
Message generated for change (Comment added) made by rhettinger
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Category: Python Library
Group: None
>Status: Closed
>Resolution: Rejected
Priority: 5
Submitted By: ChristianJ (cybb20)
Assigned to: Nobody/Anonymous (nobody)
Summary: hashable and mutable functions
Initial Comment:
It is not easy to check if an object is hashable, ie
hasattr(list(), '__hash__') -> True
try: hash(list())
except TypeError: pass
seems to be a possible way to see if an object is
hashable, however it is not satisfiable that this
information needs to be retrieved by using exception
handling.
My proposal:
There should be a hashable(obj) function returning a
bool object and additionally it would be nice to have
something like ismutable(obj) function, possibly as
built-in functions.
Reason:
callable() is a built-in function and returns
information about an object whether it's callable or
not, that is a basic info about this object.
If an object is hashable or mutable is a state of an
object that is also very important to know.
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>Comment By: Raymond Hettinger (rhettinger)
Date: 2005-09-22 04:20
Message:
Logged In: YES
user_id=80475
Adding a third -1 from me and closing the RFE.
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Comment By: Michael Hudson (mwh)
Date: 2005-09-22 03:16
Message:
Logged In: YES
user_id=6656
def ishashable(ob):
try:
hash(ob)
return True
except TypeError:
return False
is the only reasonable way to implement this function (incidentally, do you
know how hasattr works?).
I don't see the need for a builtin, but am not feeling bolshy enough to just
close the tracker item. Maybe someone else does.
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Comment By: Reinhold Birkenfeld (birkenfeld)
Date: 2005-09-22 01:27
Message:
Logged In: YES
user_id=1188172
> try: hash(list())
> except TypeError: pass
>
> seems to be a possible way to see if an object is
> hashable, however it is not satisfiable that this
> information needs to be retrieved by using exception
> handling.
Why?
> My proposal:
> There should be a hashable(obj) function returning a
> bool object and additionally it would be nice to have
> something like ismutable(obj) function, possibly as
> built-in functions.
How should "ismutable" be implemented?
> Reason:
> callable() is a built-in function and returns
> information about an object whether it's callable or
> not, that is a basic info about this object.
> If an object is hashable or mutable is a state of an
> object that is also very important to know.
It's easier to ask for forgiveness than permission.
Even callable() has been called a mistake. Just call
it and see where you come.
So, -1.
----------------------------------------------------------------------
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