Can a simple a==b 'hang' in and endless loop?
steve at holdenweb.com
Wed Jan 18 15:47:42 CET 2006
Claudio Grondi wrote:
> Yes, I know about 'is',
> but I mean, that it is not possible to use 'is' as replacement for '=='
> operator to achieve in Python same behaviour as it is the case in C and
> fails to give fully predictable results when applied to elements of
> lists in case there exist duplicate objects with same 'value' i.e. e.g.
> there are two different objects storing the integer value 1, what I mean
> can happen when there is enough other code between the Python code lines
> assigning the integer value 1 to a list element or any other identifier.
Perhaps you could try again in English? :-) Sorry, that's a very complex
sentence and it isn't clear what yo mean.
In C, of course, a == b requires that a and b be of compatible types and
that they have the same value. This means that if they are pointers they
must point to the same thing (which is exactly what "is" tests for).
> Or is there in Python a 100% reliable mechanism assuring, that there is
> one and _only one_ object carrying a given 'value' (at least for the
> built in types as integer, long integer, string, float) and if this
> value is to be assigned to a list element or any other literal the
> already existing object (if any) will be found and used/referenced?
No more than there is in C or, presumably, Java.
If you want to test for identity, use "is". If you want to test for
equality, use "==". Of you want to test for something else, kindly
explain what you want to test for.
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC www.holdenweb.com
PyCon TX 2006 www.python.org/pycon/
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