I have a variable a, and I want a to be added with b, like so:  a = a + b   Now, I have my program set up like so:  a = 2 b = 3  def add() :     a = a + b     print(str(a))  add()   Every time I run this, I get  Traceback (most recent call last): File "&lt;stdin&gt;", line 8, in &lt;module&gt; File "&lt;stdin&gt;", line 5, in add UnboundLocalError: local variable 'a' referenced before assignment   instead of  5   Please explain the obvious mistake that I am making.
How can I create or use a global variable in a function?  If I create a global variable in one function, how can I use that global variable in another function? Do I need to store the global variable in a local variable of the function which needs its access?
In how many ways can you choose $k$ numbers out of $\{1,2,3,\dots,n\}$ so none of them is consecutive? Is $\frac{1}{\sqrt{2}}$ a fraction or not? Java: splitting a comma-separated string but ignoring commas in quotes Where can game assets for Blender be downloaded? Is there any place where I can download surroundings of a game as a 3d model or maybe there re some inspired artists where they put them for download. I'm trying to find rooms from Wall-e. Some rooms, or outside surroundings or some interior surroundings. Where can I find things like that? The direction of static friction? I am constructing a thought experiment about a spinning object that is floating in intergalactic space.  I assume that this object is about the size of a planet so that it will have enough gravity so that a Foucault pendulum will work, although I'm not sure that this is necessary for the thought experiment.    I can easily determine that this object is spinning if I stand on the object and observe the galaxies around me rise and set.  Similarly, I can determine the axis of rotation.    For simplicity, I go to one of the poles of my object, and I set up my Foucault pendulum.  What will I see?  And why will I see it?  I assume that in intergalactic space, the gravity is very small (galaxies are very far away, and the mass of my object is very small compared to the mass of a galaxy) so that there will be little coupling between the gravitational field of my object and the gravitational field of the galaxies around me. Why does one get an illusion as moon following him? When you run or ride bike at night if you observe the moon you feel like he moves along with you as the same speed you are going. Why? Overleaf does not compile after using Biblatex I have my PhD deadline on Monday and disaster has struck at the very last minute! Any assistance would be eternally appreciated.  I'm using Overleaf (v2) to write my thesis - it's a very large file tree containing multiple .tex files.  Everything was compiling fine, until I decided to experiment and use:  \usepackage{biblatex}   It compiled with this included but looked odd, so I deleted the line again. However, now it does not compile - despite the document being exactly the same as before the problem began. See permissions for new files on a given directory I don't understand how my Linux machine is operating on new files.   I have an Amazon Linux AMI (RHEL based distro) and when I execute umask I get 0002, so I get whenever I create new stuff other users won't get write access.  But then I go to my home directory and I type:  $ mkdir myDir $ touch myDir/myFile $ ls -l | grep myDir   and I get  drwxrwxr-x 2 myself myself 4096 May 11 22:37 myDir   and for the folder:  $ ls -l myDir -rw-rw-r-- 1 myself myself 0 May 11 22:37 myFile   So apparently there's more going on there then my umask, since myFile permissions are more restrictive than just write protection.  Digging deeper, if I try:  $ sudo touch /var/run/myPidFile.pid $ ls -l /var/run/ | grep myPidFile.pid -rw-r--r-- 1 root    root       0 May 11 22:42 myPidFile.pid   So myPidFile.pid gets a much more restrictive default permission, under /var/run then myFile gets under my home folder.  We could blame the root umask but if I run umask under root I get 0022 which is indeed more restrictive then my user's 0002 umask but still doesn't explain how the execution bit permission isn't set.  So how can I understand a folder's default permission on Linux? I want to use a very long USB cable to place a webcam in a different room. The maximum length that I found was five meters.   What is the maximum length of a USB cable? What is the maximum length achievable when using USB extension cables? Syntax error while defining an array as a property of a class How to install Broadcom wireless drivers offline? I have installed Ubuntu alongside Windows 8.1. But the wifi is not working in Ubuntu (perhaps the drivers are not present), which worked fine in windows. Also I cant connect with Ethernet since my laptop does not have an Ethernet port. So is there any way for me to connect to the internet in ubuntu? Edit: Output of the terminal command  lspci -knn | grep Net -A2:  vikram@vikram-Inspiron-11-3148:~$ lspci -knn | grep Net -A2 01:00.0 Network controller [0280]: Broadcom Corporation BCM43142 802.11b/g/n [14e4:4365] (rev 01)     Subsystem: Dell Device [1028:0018]     Kernel driver in use: bcma-pci-bridge vikram@vikram-Inspiron-11-3148:~$    I did what Pilot6 suggested. Here is the output:    vikram@vikram-Inspiron-11-3148:~$ sudo dpkg -i *.deb [sudo] password for vikram:  Selecting previously unselected package bcmwl-kernel-source. (Reading database ... 163804 files and directories currently installed.) Preparing to unpack bcmwl-kernel-source_6.30.223.141+bdcom-0ubuntu2_amd64.deb ... Unpacking bcmwl-kernel-source (6.30.223.141+bdcom-0ubuntu2) ... Selecting previously unselected package dkms. Preparing to unpack dkms_2.2.0.3-1.1ubuntu5.14.04_all.deb ... Unpacking dkms (2.2.0.3-1.1ubuntu5.14.04) ... Setting up dkms (2.2.0.3-1.1ubuntu5.14.04) ... Setting up bcmwl-kernel-source (6.30.223.141+bdcom-0ubuntu2) ... Loading new bcmwl-6.30.223.141+bdcom DKMS files... First Installation: checking all kernels... Building only for 3.16.0-30-generic Building for architecture x86_64 Building initial module for 3.16.0-30-generic ERROR (dkms apport): kernel package linux-headers-3.16.0-30-generic is not supported Error! Bad return status for module build on kernel: 3.16.0-30-generic (x86_64) Consult /var/lib/dkms/bcmwl/6.30.223.141+bdcom/build/make.log for more information. modprobe: FATAL: Module wl not found. update-initramfs: deferring update (trigger activated) Processing triggers for man-db (2.6.7.1-1ubuntu1) ... Processing triggers for initramfs-tools (0.103ubuntu4.2) ... update-initramfs: Generating /boot/initrd.img-3.16.0-30-generic vikram@vikram-Inspiron-11-3148:~$ I'm looking for a way to reinterpret an array of type byte[] as a different type, say short[]. In C++ this would be achieved by a simple cast but in C# I haven't found a way to achieve this without resorting to duplicating the entire buffer.  Any ideas? Where do I report people for deleting their questions on purpose after they get an answer Today I was looking at the question of this . The question was pretty simple, he was looking for the eval function in  not knowing of it's existence. He received a comment and while I was finishing reading the question, I saw him commenting      Thanks, eval() is what I was looking for.   and then he deleted his question. In my opinion, such behavior isn't appropriate. So, should I just ignore this or can I do something about it? Show that the following series of function defines a continuous differentiable function function in $\mathbb R$. $$\sum_{n=1}^{\infty}\frac{\sin (nx^2)}{1+n^3}.$$  We have , $|f_n(x)|=\left|\frac{\sin (nx^2)}{1+n^3}\right|\le \frac{1}{1+n^3}\le \frac{1}{n^3}=M_n \text{ (say) }$  As, $\sum M_n$ is convergent so, the given series is uniformly convergent. Also , each $f_n(x)$ is a continuous function in $\mathbb R$. So, the given series converges to a continuous function , say $f(x)$.  But how we can show that $f(x)$ is differentiable function ?  Please help... Just beginning to learn quantum mechanics and my textbook says that all pure eigenstates of the Schrodinger equation ( with a specified potential function) have a zero standard deviation for the expectation values of energy.So every measurement of the energy yields a fixed value. I've also read that pure eigenstates are physically realisable solutions in some situations ( like the infinite potential well). But wouldn't that violate the uncertainty principle? the standard deviation in expectation of energy is zero and hence $$ΔE~Δt=0.$$ Where am I going wrong? Also could someone also give me an insight as to what uncertainty in time even means? I haven't been able to grasp that concept clearly yet. "does not contain a static 'main' method suitable for an entry point" What does \s! do? 1st example:  \starttypescript [\s!serif] [paratype]   \definefontsynonym [ParatypeSerif-Regular] [\s!name:PTSerif-Regular] [\s!features=\s!default]   \definefontsynonym [ParatypeSerif-Italic] [\s!name:PTSerif-Italic] [\s!features=\s!default]   \definefontsynonym [ParatypeSerif-Bold] [\s!name:PTSerif-Bold] [\s!features=\s!default]   \definefontsynonym [ParatypeSerif-BoldItalic] [\s!name:PTSerif-BoldItalic] [\s!features=\s!default] \stoptypescript   2nd example:  \definefont[SerifS][\s!file:GenBkBasR at \smallfontsize]   Is \s! only related to fonts? Should I use it in my typescript files? How can I compute $\mathrm{Aut}(\mathbb{Z}/4\mathbb{Z}\times\mathbb{Z}/6\mathbb{Z})$? How can I compute $\mathrm{Aut}(\mathbb{Z}/4\mathbb{Z}\times\mathbb{Z}/6\mathbb{Z})$?  If $\varphi$ is one of this automorphism then $\varphi((1,0))=(1,0),(1,3),(3,3),(3,0)$ and $\varphi((0,1))=(0,1),(0,5),(2,1),(2,5)$.  So it seems to me that this groups contains 16 elements, am i right? And if I'm right there is a way to understand to which group of cardinality 16 this is isomorphic to?  EDIT: $\mathbb{Z}/4\mathbb{Z}\times\mathbb{Z}/6\mathbb{Z}\cong\mathbb{Z}/8\mathbb{Z}\times\mathbb{Z}/3\mathbb{Z}$. And $\mathbb{Z}/8\mathbb{Z}$ and $\mathbb{Z}/3\mathbb{Z}$ are characteristic (am I right?), so $\mathrm{Aut}(\mathbb{Z}/8\mathbb{Z}\times\mathbb{Z}/3\mathbb{Z})\cong\mathrm{Aut}(\mathbb{Z}/8\mathbb{Z})\times\mathrm{Aut}(\mathbb{Z}/3\mathbb{Z})\cong\mathbb{Z}/8\mathbb{Z}^*\times\mathbb{Z}/3\mathbb{Z}^*$ and this group has cardinality 8, right? Where is my mistake? Abort Ajax requests using jQuery