Claudio Grondi wrote: [snip..] > 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 > Javascript when comparing values with '=='. > 'is' does the C, Javascript job when comparing lists, but I mean it > 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
Hmmm... : >>> a = 1 >>> b = 1 >>> a is b True Doesn't work with arbitrary longs of course... > 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. > 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? > So the Java/C '==' operator sometimes works like '==' in Python and sometimes works like 'is' ? (It switches between equality and identity depending on the types being compared IIUC). My understanding is that you can't use '==' in Java to compare strings, because it is an identity test not an equality test. You have to use a string method to compare strings. This bites quite a few people... Anyway, AFAICT your problem only matters in the abstract (where you are theoretically comparing objects you haven't specified the type of and *might* want to use '==' and *might* want to use 'is'). For practical purposes '==' will do what you want, unless you deliberately create buggy code to cause a problem when you use it... Unless you can post an example of *non-buggy* code that doesn't behave how you expect ? All the best, Fuzzyman http://www.voidspace.org.uk/python/index.shtml > Claudio -- http://mail.python.org/mailman/listinfo/python-list
