I want to retrieve the filenames of all the files with .xml extension present in various subfolders in a single directory,
How do I get a list of all files (and directories) in a given directory in Python?
Summing Up A 2D Array I have studied some of Einstein's Theory of General Relativity, and I understand that it states that gravity isn't a force but rather the effects of objects curving space-time. If this is true, then why are we instructed in middle school that it is a force? Do plugin files have to follow a specific convention to be "picked up" by WordPress? Let the function $f(x)$ be differentiable  and $f'(x)$ be continuous in $\left(-\infty,\infty \right)$ with $f'(2)=14$ then evaluate the limit  $$\lim_{x\to 0}\frac{f(2+\sin x)-f(2+x\cos x)}{x-\sin x}$$  My attempt:  $\lim_{x\to 0}\frac{f(2+\sin x)-f(2+x\cos x)}{x-\sin x}$  $\lim_{x\to 0}\left(\frac{f(2+\sin x)-f(2+x\cos x)}{\sin x-x\cos x}\right)$ $\frac{\sin x-x\cos x}{x-\sin x}$$=\left(f'(2)\right)(2)=28$  Is the method used here correct How to choose the number of hidden layers and nodes in a feedforward neural network? Is there a standard and accepted method for selecting the number of layers, and the number of nodes in each layer, in a feed-forward neural network? I'm interested in automated ways of building neural networks. Improve the editing flow with predefined options for "Edit Summary" Proving $(P(AB))^2+(P(AB^c))^2+(P(A^cB))^2+(P(A^cB^c))^2\ge\frac{1}{4}$ for any events $A$ and $B$ Show that for any two events $A$ and $B$, $$(P(AB))^2+(P(AB^c))^2+(P(A^cB))^2+(P(A^cB^c))^2\ge\frac{1}{4}$$   Using the Inclusion-Exclusion formula, De Morgan's law and $P(AB^c)=P(A)-P(AB)$, I was able to expand the $\rm{l.h.s.}$ as $$(x+y)(x+y-4z)+2z(2z+1)+x(x-2)+y(y-2)+1\quad...\quad(*),$$ where $x=P(A),y=P(B)$ and $z=P(AB)$.  However I'm not being able to group the terms involved in the $\rm{l.h.s.}$ to form a 'suitable' expression and probably the way I have grouped them is not correct.  The expression $(*)$ is subject to the condition   $\max\{0,x+y-1\}\le z\le \min\{x,y\}$ and obviously $0\le x,y,z\le 1$, but I am unable to use this.      Is there an elegant/slick way to show the inequality? It probably can be shown without a lot of work and it's possible I'm missing something trivial here. Does the use of words such as 'fail', 'wrong', 'incorrect' and 'invalid' have a sufficiently negative impact on a users frame of mind to warrant the prohibition of their inclusion in the error messages generated by typical web forms?  i.e. Should we rephrase examples like these to just use positive words?  'date entered incorrectly'  or  'failed to complete registration, please see below for invalid field entries'  (PS, the examples are there to show use of the words in an error message, not to serve as examples of error messages I would use or things that need correcting in answers, I'm not looking for advice on how to write form error messages, but for information about the effect of certain words on a users frame of mind) If the order of all nontrivial elements in a group is 2, then the group is Abelian. I know of a proof that is just from calculations (see below). I'm wondering if there is any theory or motivation behind this fact. Perhaps to do with commutators?    Proof: $a \cdot b = (b \cdot b)  \cdot (a \cdot b) \cdot (a \cdot a) = b \cdot (b \cdot a) \cdot (b\cdot a) \cdot a = b \cdot a$. proper use google webmaster tools URL Parameters There are some urls like http://domain.com/user/:username and http://domain.com/post/:id on my website, the username and id is the parameter from database. I try to let google crawler more efficiently , can I use google webmaster tools &gt; URL Parameters &gt; add parameter ? I read the document but still don't get it how to set up? the column Parameter and the rest what should I filled? or this tools only for get method parameter? Reset Windows 10 from USB I have a Windows machine (laptop) that needs fixing. The current installation is really badly broken (e.g. the taskbar is unresponsive, but the Explorer windows work, booting takes literally half an hour) and when I try to access the settings app and click on the tile to access the reset settings it instantly crashes. The same happens in Safe Mode.  I have created a USB install medium using the tool offered by Windows on my own Windows desktop machine. I've ensured that both the laptop and the USB tool have the same version of Windows (Home, 64-bit, NL). When I want to reinstall Windows on the laptop with this stick I am asked to enter a serial number which I obviously don't have. I don't want to try and see if I can phone activate it, because if it fails the install is gone.  I need to reinstall this Windows machine from a USB stick. There are a few problems I can't find an immediate solution for on the .   If I use a tool such as  to extract the serial number, will this work? If the above does not work, how can I reinstall this Windows machine? I know that it holds for $n=5$, so the first step is done.  For the second step, my IH is: $4^n &gt; n^4$, and I must show that $4^{n+1} &gt; (n+1)^4$. I did as follows:  $4^{n+1} = 4*4^n &gt; 4n^4$, and if I show that $4n^4 &gt; (n+1)^4$ holds for $n\geq 5$ I'm done, so I expand the right hand side and arrive to:  $$4n^4 &gt; n^4 + 4n^3 + 6n^2 + 4n + 1$$  And this holds iff: $$3n^4 - 4n^3 - 6n^2 - 4n - 1 &gt;0$$ And here I'm stuck, I don't really know how to show that the given inequality holds. Any hints? Windows 8.1 Keeps Turning Off Automatic Updates My OS keeps turning off automatic Windows updates without even logging off or restarting the computer.  Action center icon in the task bar warns me about choosing an option for Windows update as if I haven't chosen countless times already.  It started to get really annoying to keep choosing a Windows update option 5 - 10 times a day.   I really appreciate any help you can provide on this matter.  Things I have tried so far;   I have tried  suggested by . Unfortunately didn't help my case Tried following commands; reg add "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update" /v AUOptions /t REG_DWORD /d 0 /f  and then sc config wuauserv start= auto as suggested . Googling. Tried few suggestions which didn't help my case. On the position of multiple sub and superindices Obtaining knowledge from a random forest Random forests are considered to be black boxes, but recently I was thinking what knowledge can be obtained from a random forest?  The most obvious thing is the importance of the variables, in the simplest variant it can be done just by calculating the number of occurrences of a variable. The second thing I was thinking about are interactions. I think that if the number of trees is sufficiently large then the number of occurrences of pairs of variables can be tested (something like chi square independence).  The third thing are nonlinearities of variables. My first idea was just to look at a chart of a variable  Vs score, but I'm not sure yet whether it makes any sense.    Added 23.01.2012 Motivation    I want to use this knowledge to improve a logit model. I think (or at least I hope) that it is possible to find interactions and nonlinearities that were overlooked. I would like to set the wallpaper in the login screen (Unity Greeter), how do I do that? How do I extract a single chunk of bytes from within a file? Does the Sun produce audible sound? Is there a way to unfold a mesh? Is there a way to take a mesh, cut it with seams or sharp edges and flatten it, so that the faces stay the same shape and size?  Making paper models is one aspect, where you could use that technique.  No, I'm afraid SZ0Return is not going to do it properly.  And misusing the UV-unwrap is only a last option.    Note, while it's an option to revert to Blender 2.49 which had a script to do this, I'd like a solution that I can use inside the current workspace. How can I delete an account on a specific site? My account has 20 (!) sites associated to it.  I only use it for 3-5 sites.  To reduce clutter, I would like to delete my profiles that I do not use much.  I have went through , but when I enter the profile URL as:  http://russian.stackexchange.com/users/5772/alex   it gives the error message:     oops! this isn't a link to a valid profile   What procedure do I go through to delete my profile only on certain sites?