[EMAIL PROTECTED] a écrit : (snip) > Anyone know why towards arg is True and arg is False, arg is None is > faster than arg == None ...
Perhaps reading about both the meaning of the 'is' operator might help ? the expression 'arg is True' will only eval to true if 'id(arg) == id(True)'. Now Python objects does have a truth value by themselves. So an object can eval to false in a boolean test *without* being the False object itself. For the record, True and False are late additions to the language - at first, it only had truth values of objects, basically defined as 'empty sequences and containers, numeric zeros and None are false, anything else is true unless either: - the class implements the __len__ magic method and len(obj) == 0 - the class implements the magic method __non_zero__ (IIRC) and this obj.__non_zero__ returns false. So the common idiom is to test the truth value of an object, which is expressed as "if obj: " - using 'if obj == True:' being redundant and 'if obj is True:' usually not what you want. wrt/ None: Since being None is not the same thing as being false (even if the first imply the second) - there may be cases where you want to distinguish between an object with a false truth value from the None object itself - so you can't just use 'if not obj:'. Now since None is garanteed to be a singleton, it defines it's __cmp__ (the magic method for '==') as an identity test. So directly using the identity test is faster since it yields the exact same result as the equality test without the overhead of the additional method call. -- http://mail.python.org/mailman/listinfo/python-list
