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Prove the divisibility test by $7,11,13$ for numbers more than six digits How do you handle "that that"? The double "that" problem How can I get my external IP address in a shell script? Setting Objects to Null/Nothing after use in .NET Quoting backslashes in Python string literals I have a string that contains both double-quotes and backslashes that I want to set to a variable in Python. However, whenever I try to set it, the quotes or slashes are either removed or escaped. Here's an example:  &gt;&gt;&gt; foo = 'baz "\"' &gt;&gt;&gt; foo 'baz ""'   So instead of baz "\" like I want I'm getting baz "". If I then try to escape the backslash, it doesn't help either:  &gt;&gt;&gt; foo = 'baz "\\"' &gt;&gt;&gt; foo 'baz "\\"'   Which now matches what I put in but wasn't what I originally wanted. How do you get around this problem? Access to our computer (not only to the internet) needs to be restricted for the accounts of my kids (7, 8) until they are old enough to manage this by themselves. Until then we need to be able to define the following:   the hours of the day when computing is o.k. (e.g. 5 - 9 pm) the days of the week when computing is not o.k. (e.g. mondays to fridays) the amount of time allowed per day (e.g. 2 hours)   In 11.10 all of the following that used to do the job don't work any more:   : for > 11.10 no more available through the ppa. : command line alternative, but from 11.10 removed from the repositories. : Looks great but repeatedly crashes to force restarting X-server. So we can't use or recommed this program at the moment.   Are there any other alternatives? I am wondering if the mass density profile $\rho(\vec{r})$ has been characterized for atomic particles such as quarks and electrons. I am currently taking an intro class in quantum mechanics, and I have run this question by several professors. It is my understanding from the viewpoint of quantum physics a particle's position is given by a probability density function $\Psi(\vec{r},t)$. I also understand that when books quote the "radius" of an electron they are typically referring to some approximate range into which an electron is "likely" to fall, say, one standard deviation from the expectation value of its position or maybe $10^{-15}$ meters.  However it is my impression that, in this viewpoint, wherever the particle "is" or even whether or not the particle "had" any position to begin with (via the Bell Inequalities), it is assumed that if it were (somehow) found, it would be a point mass. This has been verified by my professors and GSIs. I am wondering if its really true.  If the particle was truly a point mass then wherever it is, it would presumably have an infinite mass density. Wouldn't that make electrons and quarks indistinguishable from very tiny black holes? Is there any practical difference between saying that subatomic particles are black holes and that they are point masses? I am aware of such problems as Hawking Radiation although at the scales of the Schwarchild radius of an electron (back of the envelope calculation yields $\tilde{}10^{-57}$ meters), would it really make any more sense to use quantum mechanics as opposed to general relativity?  If anyone knows of an upper bound on the volume over which an electron/quark/gluon/anything else is distributed I would be interested to know. A quick Google Search has yielded nothing but the "classical" electron radius, which is not what I am referring to.  Thanks in advance; look forward to the responses. How to duplicate sys.stdout to a log file? Edit: Since it appears that there's either no solution, or I'm doing something so non-standard that nobody knows - I'll revise my question to also ask: What is the best way to accomplish logging when a python app is making a lot of system calls?  My app has two modes.  In interactive mode, I want all output to go to the screen as well as to a log file, including output from any system calls.  In daemon mode, all output goes to the log.  Daemon mode works great using os.dup2().  I can't find a way to "tee" all output to a log in interactive mode, without modifying each and every system call.    In other words, I want the functionality of the command line 'tee' for any output generated by a python app, including system call output.  To clarify:   To redirect all output I do something like this, and it works great:  # open our log file so = se = open("%s.log" % self.name, 'w', 0)  # re-open stdout without buffering sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)  # redirect stdout and stderr to the log file opened above os.dup2(so.fileno(), sys.stdout.fileno()) os.dup2(se.fileno(), sys.stderr.fileno())   The nice thing about this is that it requires no special print calls from the rest of the code.  The code also runs some shell commands, so it's nice not having to deal with each of their output individually as well.  Simply, I want to do the same, except duplicating instead of redirecting.  At first thought, I thought that simply reversing the dup2's should work.  Why doesn't it?  Here's my test:   import os, sys  ### my broken solution: so = se = open("a.log", 'w', 0) sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)  os.dup2(sys.stdout.fileno(), so.fileno()) os.dup2(sys.stderr.fileno(), se.fileno()) ###  print("foo bar")  os.spawnve("P_WAIT", "/bin/ls", ["/bin/ls"], {}) os.execve("/bin/ls", ["/bin/ls"], os.environ)   The file "a.log" should be identical to what was displayed on the screen. Close and flag links do nothing on mobile site Set the size of pgf picture? I have a pgf picture which I insert with:  \input{m1.pgf}   But the image is too big. Instead of regenerating a smaller image, I'd rather take advantage of vector graphics, and have XeLaTeX scale it. How do I set the width of pgf picture (keeping its aspect ratio)?  MWE  tex:  \documentclass{article}  \usepackage{fontspec} % enagles loading of OpenType fonts \usepackage{polyglossia} % support for languages  % fonts: \defaultfontfeatures{Scale=MatchLowercase,Mapping=tex-text} % without this XeLaTeX won't turn "--" into dashes \setmainfont{DejaVu Sans} \setsansfont{DejaVu Sans} \setmonofont{DejaVu Sans Mono}  % pgf: \usepackage{pgf}  \begin{document}  \input{m1.pgf}  \end{document}   Sample pgf:  (it's too big to cite it here, and I can't make much smaller). Person, Persons, People, Peoples Showing two ring homomorphisms that agree on the integers must agree on the rationals I have two ring homomorphisms $f,g\colon \mathbb{Q}\to X$. I know that $f=g$ on the integers. How can I show that $f$ and $g$ agree on the rationals?   My attempt:  let $x,y \in \mathbb{Z}$, $y\neq 0$.  $$\begin{align*} f(x/y)&amp;=f(x)f(1/y) &amp;&amp;\text{because }f\text{ is a ring homomorphism}\\  &amp;=g(x)f(1/y) &amp;&amp;\text{because }f\text{ and }g\text{ agree on the integers} \end{align*}$$  I do not know how to rewrite $f(1/y)$ so that I can replace it with $g(1/y)$. Any hints will be much appreciated. Thanks. How do you make a torus 'telescope' open? ContentVersion Content-Type I need to stream a file from Salesforce in our webapplication. To make sure the file is properly opened, I have to set Content-Type header.  How to retrieve the Content-Type (MIME) of a file?  I expect values like: image/png, application/pdf, text/html etc.  How to get these values? I am using the Java and a SOAP client to retrieve the data. Can any one explain me what is the use of derivatives in real life. When and where we use derivative, i know it can be used to find rate of change but why?. My logic was in  real life most of the things we do are not linear functions and derivatives helps to make a real life functions into linear.  eg converting parabola into a linear function $x^{2}\rightarrow 2x$  but then i find this; derivation of $\sin{x}\rightarrow \cos{x}$  why we cant use $\sin{x}$ itself to solve the equation. whats the purpose of using its derivative $\cos{x}$. Please forgive me if i have asked a stupid questions, i want to improve my fundamentals in calculus. Uk tourist visa - duration of stay My mother is given a UK tourist visa for 2 years with a duration of stay as 180 days. It is a c type multiple entry visa. Is this 180 days is the total stay she can take or is it duration of stay per visit.  Thanks in advance for your reply. Is it possible to wipe an entire iCloud Photo Library? I've been using the beta iCloud Photo Library for a week and a bunch of photos got duplicated and I'd like to wipe all the photos out and start over.  I have backups of all the photos and have turned off iPhoto Cloud Library on all iOS devices. When I log into the web app - it still shows dozens of albums and I can delete all the photos, then go to deleted items and then purge them, but the ghost albums are still there messing things up.  I've turned off the library entirely and you can see there is a 30 day waiting period.     If I click on albums, there are pages of them and no delete button anywhere. If I turn on the library on an iOS device, data starts flooding back as if I wanted to recover the photos.  I don't want to recover anything, I want a clean wipe and clean slate.  Currently, there are 7807 photos in the deleted album and no way to mass delete them. I have 31 albums that show up in iCloud and no way to delete them.  Is there some way to accelerate this or must people wait a month for a corrupt library to eventually be purged to start over?  (I have tickets open with AppleCare after  and it's escalated to engineering, but I was informed that it might be a week or two before it gets seen :-( Perhaps someone has a better idea to clear things out or noticed something I've missed.) How to input integer value to an array, based preceeding row + column values? Why do paintbrush loops get thicker at the top in Illustrator? When I do swirls in Illustrator with the paintbrush tool I often get this result (see image).    The loops doesn't get perfectly rounded, instead sometimes some of them gets thicker at the top of the loop... It tends to happen more if I paint small with low brush sizes. Why is this happening? How do I install Ubuntu?