Is there a meaningful difference between  if self.pk is not None:   and   if self.pk:   when checking a model field in python django?  Other languages have all kinds of differing 'correct' ways to check for a variable being null, empty, nonexistant, whatever.   a) I don't know how python handles the check  b) I don't know if this is important and / or meaningful in the context of django model fields
I've seen several examples of code like this:  if not someobj:     #do something   But I'm wondering why not doing:  if someobj == None:     #do something   Is there any difference? Does one have an advantage over the other?
Class vs Struct for data only? Is there any advantage over using a class over a struct in cases such as these?  (note: it will only hold variables, there will never be functions)  class Foo {  private:       struct Pos { int x, y, z }; public:        Pos Position;  };   Versus:  struct Foo {    struct Pos { int x, y, z } Pos; };     Similar questions: Is $0\,\mathrm{m}$ dimensionless? Is $0 \, \mathrm m = 0 \, \mathrm s = 0 \,\mathrm {kg} = 0$? How do we define $[0 \, \mathrm m]$?  I once was given an assignment where I was asked to deduce and write down some physical quantity. It turned out that this quantity was $0$ in one unit or another, so I decided to drop the physical units because I figured that it didn't matter anyhow.  But I got to thinking:  If $0 \, \mathrm m = 0$, then we could add units of different dimensions (an operation not normally defined) like so: $5 + 0 \,\mathrm m = 5$.   Does $[ \cdot ]$ map $0 \, \mathrm m$ to both $0$ and $L$? Is there an established regime of thinking about physical quantities as an abstract algebra? Perhaps as a vector space where formal sums such as $5 \, \mathrm m + 10 \, \mathrm s$ are allowed? Would it be improper to drop the units of measurement of $0 \,\mathrm m$ like this in an academic paper? How to make files protected? I'm looking to find records in a table that match a specific number that the user enters.  So, the user may enter 12345, but this could be 123zz4-5 in the database. I imagine something like this would work, if PHP functions worked in MySQL. SELECT * FROM foo WHERE preg_replace(&quot;/[^0-9]/&quot;,&quot;&quot;,bar) = '12345'  What's the equivalent function or way to do this with just MySQL? Speed is not important. Maximal Ideals in Ring of Continuous Functions Dummit and Foote, 7.4.33(a): Let $R$ be the ring of all continuous functions $[0,1] \to \mathbb{R}$ and let $M_c$ be the kernel of evaluation at $c \in [0,1]$, i.e. all $f$ such that $f(c) = 0$. Show that if $M$ is a maximal ideal in $R$ then $M = M_c$ for some $c$.    I am aware of proofs that use the compactness of $[0,1]$; however I have been told that a simpler proof exists using only the isomorphism theorems for rings along with basic facts about ideals. I have tried on my own to prove it this way but still have no success; is it possible?  (My attempts go something like: since $M$ is maximal, the quotient ring $R/M$ is a field. Then it would be nice to use the fact that $R/M$ has no zero divisors, but I can't quite make it work. Alternatively, consider $M \cap M_c$.) ''More than one row returned by a subquery used as an expression'' postgres error I am trying to realize a postgres request :   select distinct nom_reg_12  from region_15,repartition  where st_intersects(region_15.geom,                    (select geom                     from repartition                     where id_espece='Tetrarti'))=true;    but i get the following error :      More than one row returned by a subquery used as an expression   in the first time I tried this and it work fine :   select distinct nom_reg_12  from region_15,repartition  where st_intersects(region_15.geom,repartition.geom)=true;   and then I tried this a part to get the geometry I want :   select geom from repartition where id_espece='Tetrarti' I have, by default, 250MB of swap space in Ubuntu, and I want to expand it to a larger size. I need 800MB, which I think will be enough to open several applications without having to hit the current limit of swap. I hope someone can help me. Shows "unable to locate package unzip" error I have installed Ubuntu 12.04 server , shows    E:unable to locate the package unzip   the above error is also shown, if I try to install packages also. Can any one help me out to get out from this error. After parsing collada files I found out that we have to load two(or more) indices each pointing to say a vertex or normal etc. like this (&lt;p>3 0 2 0 0 0&lt;/p>)  Is there a way to load (and use)these indices to indices buffer(ELEMENT_ARRAY_BUFFER) like this (vnvnvn...) ; where v is vertex pointer, n is normal pointer from the above. with vertices loaded to VBO1 like (vvvv...) and in VBO2 like (nnnn...). So that we dont have to repeat the normals in VBO2.  VBO like (vnvnvn...) is also ok. (and not something like this ), I'm not trying to use multiple indices buffer. I'm trying to put all the given indices into one index buffer and use them alternately.  (If I wasnt clear i will try for more clarification.) How can I mount my partition with executive permissions using the launcher icons? complex polynomial satisfying inequality What's the difference between "established" and "founded" In this sentence: "CARE was ...... in 1945 to help people after World War II."    A. founded  B. built C. established D. constructed    The answer is C. But why don't we use "founded" in this case, I think they have the same meaning. Can you help me to give a reason for that? Extreme Points of a Convex Hull "In a party people shake hands with one another" Financial requirements to sponsor relatives visiting the Schengen area [Germany]? says:  SSH_ASKPASS    If  ssh needs a passphrase, it will read the passphrase from the    current terminal if it was run from a terminal.  If ssh does not    have  a  terminal associated with it but DISPLAY and SSH_ASKPASS    are set, it will execute the program  specified  by  SSH_ASKPASS    and open an X11 window to read the passphrase.   I'd like SSH to use an askpass program even if it was run from a terminal.  On occasion, I have to connect to servers, where there's some delay in showing a password prompt (maybe due to network issues, maybe due to attempted reverse DNS lookups, …). I get annoyed and switch to something else, and forget about the attempted connection. (Insert joke about attention span of a goldfish.) When I finally get back to it, the prompt's timed out and even a correct password would just result in a closed connection.  Keys would be one solution, but not every system I use has my usual SSH keys. However, I usually use Ubuntu systems, and Ubuntu has an SSH askpass program installed by default.  If an askpass window popped up, however, I'd be immediately aware of it. That's a good enough compromise for me, if only I can get it to work. This question was triggered by .  Basically, it goes like this: If you have a weapon with a certain magical effect, let's say the minor property unbreakable (can not be broken, requires special means) or temperate (no harm in temperatures between -20 to 120 F), it can bypass the immunity of something like a Werewolf because it is magical instead of mundane. This goes for any minor property because those properties are under the Magic Items portion of the DMG on pg.143.  How does this differ from a pair of gauntlets with the exact same effect being used as an improvised weapon (emphasis added for clarity) from dealing damage in the same manner to the same Werewolf? Or something that's clearly not a weapon like a Shield of Missile Snaring being used to bash an opponent? Property of the conjugate transpose matrix with inner product Adding Table to Layout View using ArcPy? I am using ArcGIS 10.1 and I have a non-spatial table and some layers in a Data Frame.   When I switch to Layout View I want to be able to show the map in a data frame element and the table in another element (something that one could do with "Add Table To Layout" from Table Options, but I want to do this in one step without having to go to Table Options).   Is there a way to do this using ArcPy?   I couldn't find any function in the ArcPy library that would create a new Layout Element ... and then I also don't know how to add the contents of the table to the Layout Element. What is the technical term for when people thinks the actions of the few represent the many.  Like when people thinks everyone in a specific group behaves a certain way cause of how a few people in the group behave, including non stereotypical behaviours. I thought it was "generalisation" but I couldn't find any articles using that term.