Convert seconds to hh:mm:ss in Python
How do I convert seconds to hours, minutes and seconds?
How to find out if a file exists in C# / .NET? I would like to test a string containing a path to a file for existence of that file (something like the -e test in Perl or the os.path.exists() in Python) in C#. What are the general rules regarding when can you refreeze food that was frozen and then thawed in the fridge? and what are the reasons behind them? (Hygiene? Food quality?). Let's assume for the sake of the argument that the items were in a non-frozen state only a few hours.  To be more specific, I'm interested in the application of these rules for  - Ginger garlic paste - Dough - Indian Curries - Green Chilly paste - Frozen green peas Is there a difference between single and double quotes in Java? Has the speed of light changed over time? Could someone judge my (stoner) hypothesis that the speed of light has changed over time -- i.e. as the universe has expanded in volume light has slowed down, perhaps going so far as back to the big bang when it was infinitely fast and there was no time because everything happened at once etc. Thinking that the speed at which information can propagate through the universe is linked to the size of it seems intuitive to me. My question -- is there an easy disproof of this? Would Einstein have to be wrong? Does it violate anything supposedly more fundamental such as quantum or string theories? Do any current experiments invalidate it? If not can you show me in any case why you think its unlikely.   Edit 8/24  I'm accepting Mark M.'s answer but will post this here because there is a character limit on comments  @Mark M thanks, good answer but as someone who has only read some popular physics, and should leave this to the experts, I'm still muddled in my personal theory. I don't see why you should need two units to measure the speed of light. The thing I have a hard time wrapping my head around is the relation of time and distance. They seem like they could fundamentally be the same thing. If you say time is measured fundamentally by the vibration of so and so quantum object in space... why can't we just measure that vibration distance as the constant... I'll repeat myself to try to be clear... there is a certain minimum distance that particles have to go to interact with each other... if it wasn't vibrating there wouldn't be time,its what creates the illusion of time...so instead of talking about speed or c as distance/time.... can't we simply talk about that distance a quantum object vibrates....I'll lead up to my point.....perhaps there can need be only one constant here, and that is the physical size of the universe. a tiny metal tuning fork doesn't appear to be vibrating at all but if you blew it up to the size of the empire state building the metal rods would move from window to window. perhaps as our universe expanded in size the length of that minimum vibration (perhaps infinite at point zero) would have expanded, and therefore created the illusion of time and the speed of light, which, as the universe expands, will continue slowing down. perhaps we are like a big balloon and we have been blown up and all the fields/particles-without-size are vibrating more and more in that space.. am i missing something obvious here? Enumerations on PHP I know that PHP doesn't yet have native Enumerations. But I have become accustomed to them from the Java world. I would love to use enums as a way to give predefined values which IDEs' auto-completion features could understand. Constants do the trick, but there's the namespace collision problem and (or actually because) they're global. Arrays don't have the namespace problem, but they're too vague, they can be overwritten at runtime and IDEs rarely know how to autofill their keys without additional static analysis annotations or attributes. Are there any solutions/workarounds you commonly use? Does anyone recall whether the PHP guys have had any thoughts or decisions around enumerations? Are there any free/open source alternatives to Adobe After Effects? I've been a illustrator and graphic designer for a number of years and now I'm looking to go more into motion graphics and visual effects. Is there anything that is open source/free (not a demo, education version or trial) that is as complex and feature-rich as Adobe After Effects but for Linux? I've tried Cinlerra, kdenlive, openshot and Blender and whilst they are good at video editing (and 3d modelling in Blender's case) they fall short in effects and compositing features.  I've also tried , but the project recently closed and the last update was quite buggy.  Also,  doesn't work and hasn't been updated in many many years, so don't mention it ;-) Why is the speed of light defined as 299792458 m/s? Why is the speed of light defined as $299792458$ $m/s$? Why did they choose that number and no other number?  Or phrased differently:  Why is a metre $1/299792458$ of the distance light travels in a sec in a vacuum? I made an svg in Illustrator, but now I want to use it in a website/app but it's a huge size (around 10 MB) how can I decrease the size of it? My illustrator file is pretty big but that because I have some tracing elements underneath. The file also has a big artboard, but when I save should I delete my tracing elements, and decrease the artboard size? Get the name of an object's type Martingale formulation of Bellman's Optimality Principle From David Williams' Probability with Martingales     Related question:   What I tried: For no 2, if $\ln Z_n - n \alpha$ is a supermartingale, then for $m &lt; n$, $$E[\ln Z_n - n \alpha | \mathscr F_m] \le \ln Z_m - m \alpha$$ $$ \to E[\ln Z_N - N \alpha | \mathscr F_0] \le \ln Z_0 - 0 \alpha$$ $$ \to E[\ln Z_N - N \alpha] \le \ln Z_0$$ $$ \to E[\ln \frac{Z_N}{Z_0}] \le N \alpha$$ Is that right?  For no 1, for $m &lt; n$, $$E[\ln Z_n - n \alpha | \mathscr F_m] = E[\ln Z_n | \mathscr F_m] - n \alpha$$ $$ = E[\ln \frac{Z_n}{Z_0} | \mathscr F_m] - n \alpha + \ln Z_0$$ $$ = E[\ln \frac{Z_n}{Z_{n-1}} | \mathscr F_m] + ... + E[\ln \frac{Z_{m+1}}{Z_{m}} | \mathscr F_m]$$ $$+ \ln \frac{Z_m}{Z_{m-1}} + ... + \ln \frac{Z_{1}}{Z_{0}} - n \alpha + \ln Z_0$$ Note that $$Z_n - Z_{n-1} \le |Z_n - Z_{n-1}| \le C_n |\epsilon_n - \epsilon_{n-1}| \le 2C_n \le 2Z_{n-1}$$ Also, I think $$\ln \frac{Z_n}{Z_{n-1}} \le |Z_n - Z_{n-1}|$$ Hence we have $$E[\ln \frac{Z_n}{Z_{n-1}} | \mathscr F_m] + ... + E[\ln \frac{Z_{m+1}}{Z_{m}} | \mathscr F_m]$$ $$+ \ln Z_m - n \alpha$$ $$\le E[2Z_{n-1} | \mathscr F_m] + ... + E[2Z_{m} | \mathscr F_m]$$ $$+ \ln Z_m - n \alpha$$ $$= 2(E[Z_{n-1} | \mathscr F_m] + ... + E[Z_{m} | \mathscr F_m])$$ $$+ \ln Z_m - n \alpha$$ One thing to do would be to show that $$2E[Z_{n-1} | \mathscr F_m] + ... + 2E[Z_{m} | \mathscr F_m] \le (n-m) \alpha$$ possibly by showing that $2E[Z_{\{\cdot\}} | \mathscr F_m] \le \alpha$ How would I do that? Something else: $$E[\ln \frac{Z_n}{Z_m} | \mathscr F_m] + \ln Z_m - n \alpha$$ $$ \le E[|Z_n - Z_m| | \mathscr F_m] + \ln Z_m - n \alpha$$ $$ \le E[2Z_m | \mathscr F_m] + \ln Z_m - n \alpha$$ $$ \le 2Z_m + \ln Z_m - n \alpha$$ Now $2Z_m \le (n-m) \alpha?$ We have $$2Z_m = 2\sum_{k=1}^{m} C_k(\epsilon_k - \epsilon_{k-1})$$ $$\le 2\sum_{k=1}^{m} Z_{k-1}$$ I'm not quite sure how to show that $$2\sum_{k=1}^{m} Z_{k-1} \le (n-m)\alpha$$ if that's even true. How can/else can I approach this problem?  For no 3, no idea. Any hints? I think it has something to do with a stopping time. Might we have to use the ff lemma (red box):    ? How does one prove that every finite group is isomorphic to a subgroup of an alternating group? A Product function for matrix products The label toolbar uses fields in the attribute table of vector layers to fine tune labeling (Data defined labeling). That's the main reason i'm looking for that, but it may have more applications.  I'd like to automatically add some format columns instead of adding them manually every time.   Do you know a plugin or a way to do this manipulation automatically on multiples layers ?  I tried to get the QGIS tool "Add a field to attribute table" into a quick model which works properly, but it creates a new memory layer. And I'd like just new fields.  ##Add_ETIKT_Field=name ##myvlayer=vector ##myvlayer=output vector outputs_QGISADDFIELDTOATTRIBUTESTABLE_2=processing.runalg('qgis:addfieldtoattributestable', myvlayer,'ETIKT_Y',1,15.0,4.0,None) outputs_QGISADDFIELDTOATTRIBUTESTABLE_1=processing.runalg('qgis:addfieldtoattributestable', outputs_QGISADDFIELDTOATTRIBUTESTABLE_2['OUTPUT_LAYER'],'ETIKT_X',1,15.0,5.0,myvlayer)   What I'm looking to automate is :   Open the attribute table Edit button Field Calculator button Add Column + Type + length + Precision   It seems there's some ideas in , but I'd love to avoid coding anything, or at least at minimum go through the modeler.     Adding and Removing Fields       To add fields (attributes), you need to   specify a list of field definitions. For deletion of fields just   provide a list of field indexes.   if caps &amp; QgsVectorDataProvider.AddAttributes:     res = layer.dataProvider().addAttributes([QgsField("mytext", QVariant.String), QgsField("myint", QVariant.Int)])  if caps &amp; QgsVectorDataProvider.DeleteAttributes:     res = layer.dataProvider().deleteAttributes([0]) How to hook into the CPT's title placeholder? Mean and variance of inverse of a normal RV My random variable $X$ is normally distributed with mean $b$ and variance $p$. I defined a new RV, $Y$, such that $Y=1/X$. Does anyone know how to find the mean of $Y$ and $Y^2$? I forgot my password of a TrueCrypt file I used a few years ago.  How would I go about 'cracking' it? I'm not sure if there is a way to attack it or if it can only be done by brute-force. I used it on a Mac. I still have the Mac I used it on, but of course turned that off many times since I used it.   I have a passphrase that I thought would relate to this file. Maybe I used some variant of it. But might be something completely different. I have some other words that I might have used, but would need give it another thought how I could have used those.  Is there an automated way to test variations on what I think the passphrase was to regain access to the volume? Is there any other way I might regain access? Smaller membership symbol To mean that x is an element of X, we can write x \in X. However, in the standard packages, the membership symbol that results is too big; it draws too much attention to itself. This is especially evident when we're doing set theory and writing sets as lowercase, as in x \in y. Does anyone one how to draw a less attention-seeking membership symbol? I am given two charged particles of same charge at a distance of $r$. They initially apply force $F$.  Now an infinite dielectric (of dielectric constant $4$) of width $\frac{r}{2}$ is introduced between the particles. What will be the new force?   I find this problem confusing because I have only been told about forces when its either fully dielectric or fully vaccum given by Coulomb's law. How do we get forces when only partial space is dielectric? Please check my simplification for x? Let $f$ be a measurable function on a measure space $X$ and suppose that $fg \in L^1$ for all $g\in L^q$. Must $f$ be in $L^p$, for $p$ the conjugate of $q$? If we assume that $\|fg\|_1 \leq C\|g\|_q$ for some constant $C$, this follows from the Riesz Representation theorem. But what if we aren't given that such a $C$ exists?