On Monday, March 3, 2014 3:12:30 PM UTC+5:30, ast wrote: > hello > Consider following code:
> >>> A=7 > >>> B=7 > >>> A is B > True > I understand that there is a single object 7 somewhere in memory and > both variables A and B point toward this object 7 > now do the same with a list: > >>> l1 = [1, 2] > >>> l2 = [1, 2] > >>> l1 is l2 > False > It seems this time that there are 2 distincts objects [1, 2] in memory. l1 > points > toward the first one and l2 points toward the second one. > if I change one, the second remains unchanged > >>> l1.append(3) > >>> l1 > [1, 2, 3] > >>> l2 > [1, 2] > I dont really understand why the behavior is different. > Both integer 7 and list [1, 2] are objects. Why is it > different ? Short answer: Avoid using 'is'. Long answer: http://www.beyondwilber.ca/healing-thinking/non-identity-korzybski.html Pragmatic answer: Think of 'is' as a short-form for 'machine-rep-is' And use machine representations with the same alacrity that a C programmer uses inline assembly -- https://mail.python.org/mailman/listinfo/python-list
