In my understanding, all things in python are object and some of them per-allocate memory to them (for int the range is from -5 to 256).  My question is if the address not per-allocate, does it create in fly?  for example:  print id(256) a = 256 print id(a)  36609008 36609008   this example indicates variable a is referring the object 256's memory, thus they have same address.   print id(300) a = 300 print id(a)  106711544 106708304   for the example above:   does python create two objects? (it seems yes) why -5 to 256? would those per-allocated object be reused to create new objects?
Why does the following behave unexpectedly in Python?  &gt;&gt;&gt; a = 256 &gt;&gt;&gt; b = 256 &gt;&gt;&gt; a is b True           # This is an expected result &gt;&gt;&gt; a = 257 &gt;&gt;&gt; b = 257 &gt;&gt;&gt; a is b False          # What happened here? Why is this False? &gt;&gt;&gt; 257 is 257 True           # Yet the literal numbers compare properly   I am using Python 2.5.2. Trying some different versions of Python, it appears that Python 2.3.3 shows the above behaviour between 99 and 100.  Based on the above, I can hypothesize that Python is internally implemented such that "small" integers are stored in a different way than larger integers and the is operator can tell the difference. Why the leaky abstraction? What is a better way of comparing two arbitrary objects to see whether they are the same when I don't know in advance whether they are numbers or not?
How to specify a short int literal without casting? Pgfplots: Linewidth when using \ref in custom legend Why didn't Doc remember Marty's outfit? In Back to the Future 3, Doc (from 1955) sends Marty back in time wearing a cowboy outfit.  But then, Doc (from 1885) doesn't remember that it was him who offered this outfit to Marty.   Does this mean there are two different Docs (from differing timelines) or is it the same Doc but he somehow forgot the outfit. Central Pennsylvanian English speakers: what are the limitations on the "needs washed" construction? Ring homomorphism and characteristic If you search for something on "all sites" (using the searchbox at the top of , you'll reach the search results, e.g.  .  If you click directly on a tag on that page, e.g.        You get 404 Page Not Found error, e.g.     Steps to reproduce   Go to  and enter e.g. "keyforge" into the "Search all sites" field. Arrive at  Click on the "keyforge" tag below a search entry. Reach  (404 page not found)   Expected behaviour  Reach   System Info  Happens in both Firefox and Vivaldi browsers on Windows 10. Adding values to a C# array How to disable Ctrl+Shift+U? Ctrl+Shift+U is a combined shortcut in Eclipse. But when I press it, it shows up a u, just like input with an underline. I guess this shortcut has been declared by Ubuntu, so I can't use it. I used to solve this problem by typing Caps Lock first. Is there any better method? How many fixed points in a permutation I am taking a probability course and we have been of course learning the classic problems of men with hats or variations of that in some other form. The problems being of the type if $n$ men have $n$ hats and mix them all together, whats the probability $0, 1, 2,$ or $k$ men choose their hat.   But from what I can gather is that they are all problems of the same type, for any given random permutation of $k$ objects how many fixed points are there. My professor taught us to solve this using conditional probabilities (conditioning on whether the first person matched and then generating a system of equations) and using the inclusion-exclusion principle. But is there any other way to reason this? Measures of residuals heteroscedasticity This wikipedia  lists a number of techniques to detect OLS residuals heteroscedasticity. I would like to learn which hands-on technique is more efficient in detecting regions affected by heteroscedasticity.  For example, here the central region in the OLS 'Residuals vs Fitted' plot seen to have higher variance than the sides of the plot (I am not entirely sure in facts, but let's assume it's the case for the sake of the question). To confirm, looking at the error labels in the QQ plot we can see that they match the error labels in the center of the Residuals plot.  But how can we quantify the residuals region that has significantly higher variance? Retail boxed Steam activated games: can they be resold? I recently purchased retail boxed versions of   Dead Island (which is awesome) Warhammer 40k: Space Marine (not so much)   I finished both games and I was thinking of reselling them or giving them to a friend to play. However, these are both Steam activated games that had a required Steam registration code I had to enter -- and validate on Steam -- as part of the installation.  If I give these games to a friend or resell them, will they even work? Is the registration code single use and tied to a single person / computer / Steam account? Database design help. many-to-many relationship How can I return to the start of a line in a console? How can I return to the start of a line and overwrite what has already been output on the console? The following does not appear to work:  System.out.print(mystuff+'\r'); What is this "answer your own question" jazz? I have created a 'control' using jQuery and used jQuery.extend to assist in making it as OO as possible.  During the initialisation of my control I wire up various click events like so  jQuery('#available input',              this.controlDiv).bind('click', this, this.availableCategoryClick);   Notice that I am pasing 'this' as the data argument in the bind method. I do this so that I can get at data attached to the control instance rather from the element that fires the click event.   This works perfectly, however i suspect there is a better way  Having used Prototype in the past, I remember a bind syntax that allowed you to control what the value of 'this' was in the event.  What is the jQuery way? How much money did Harry Potter have? So, we know Harry . By descriptions from the books, it looks like he had enough money to spend during his school years with plenty to spare for later life.  Is there an estimate on how much money he had? How much would that be in muggle money? Was he extremely rich?  I'm thinking here that he could have received more than just an inheritance. For example, anonymous supporters could have given him money through the bank while he was a baby, or when he was about to go to Hogwarts, and he wouldn't have known (not even Dumbledore would have known). An  can be identified by its  together with isolating intervals with rational bounds for its real and imaginary parts. The degree of an algebraic number is the  of its minimal polynomial. There are known algorithms that allow to easily compute sum and product of algebraic numbers in this representation, raise them to a rational power, extract real and imaginary parts, compare them, or evaluate them numerically to an arbitrary precision.  Is there an efficient algorithm that given an algebraic number $\alpha$ in this representation can decide if $\alpha$ can be represented as a sum or product of algebraic numbers of smaller degree? Is it ever acceptable for a period to come after a quote at the end of a sentence? Divisor function asymptotics Define $\tau_{r}(n) = \sum_{d_1...d_r = n}1$.   One exercise in a book on sieve theory asked for an elementary proof by induction of the fact that   $$\sum_{n\le x}\tau_r(n) = \frac{1}{(r - 1)!}x(\ln x)^{r - 1} + O\left(x(\ln x)^{r - 2}\right)$$  The base case $r = 2$ is easy with reversing the order of summation.  The only other progress that I made was the fact that $\sum_{n\le x}\tau_{r}(n) = \sum_{d\le x}\left\lfloor\frac{x}{d}\right\rfloor\tau_{r- 1}(d)$, but I don't know how to proceed. How can I get a DisplayLink USB monitor work under Ubuntu? I have a DisplayLink-based external USB monitor, which has both power and data over USB, and seems to work perfectly under Windows 7, but only can display a text console under Ubuntu 10.10, and that I can only use when I am actually switched to it. So the only Use I can have so far is to have some text-based monitoring or console that I can watch while working on the graphic display.   I know there are some development done for DisplayLink, but I never could get it to actually run properly.   Yes, I tried the detailed setup described in other , but they did not work, and instead crashed my X that I had to restore.   Merci :-)