For teaching purposes, I would like a good explanation and example of why the &quot;\&quot; is needed in searching for, say a period or a character that python may interpret differently. In the below example, I do NOT use a &quot;\&quot; to escape the &quot;.&quot; and it still works fine. def checkfordot():     dotpattern=&quot;[.]&quot;     searchingfor=input(&quot;Enter string:&quot;)     if (re.search(dotpattern,searchingfor)):         print(&quot;Has a dot&quot;)     else:         print(&quot;Does not have a dot&quot;)  Output: &gt;&gt;&gt; checkfordot() Enter string:dfsdf. Has a dot &gt;&gt;&gt; checkfordot() Enter string:ffsdfsdfsdf Does not have a dot &gt;&gt;&gt;   In this case, using dotpattern=&quot;[.]&quot; or dotpattern=&quot;[.]&quot; doesn't seem to make much difference. Can someone a) explain why the above works without an escape and a simple explanation of what the escape does and in what situations b) provide an example or ideally two examples, integrated into my code, that demonstrates well why the escape character is required and how it is used for effective searching (or vice versa, in that without the &quot;&quot; the program would not work) Ironically, in typing this out - I noticed I had to escape the \ in order for it to be printed. Here I am typing: &gt;: &quot; \ \  &quot; ....but it prints just one backslash &gt;&quot;\&quot;
I am tired of always trying to guess, if I should escape special characters like '()[]{}|' etc. when using many implementations of regexps.  It is different with, for example, Python, sed, grep, awk, Perl, rename, Apache, find and so on. Is there any rule set which tells when I should, and when I should not, escape special characters? Does it depend on the regexp type, like PCRE, POSIX or extended regexps?
Noticing that the "Human Verification" image did not show, I found that the src, , shows that sstatic.net is giving an SSL vertificate for *.stackexchange.com.. How can I modify the advanced search form when my hook runs too early? Is taking the CUA (certified Usability analyst) certification worth it? I see a lot of people taking this  nowadays and I wonder if its actually worth it and how is it received by the industry and does it really help in bringing you up to speed with UX and usability best practices. Can anyone who has taken the exam before provide inputs on its benefits and also its cons if any.  I did see the question  and David's answer did mention that he found it useful but I would like to get more context in what sense people might find it useful and how it could potentially supplement or enhance a career. How to get pixel data from a UIImage (Cocoa Touch) or CGImage (Core Graphics)? How to apply for a UK standard visitor visa as a family? What are the differences between "to talk" and "to speak"? Consider the function : $$f: \mathbb{R}^2 \rightarrow \mathbb{R} , (x,y) \mapsto   \begin{cases}         0 &amp; \text{for } (x,y)=(0,0) \\    \frac{x^3}{x^2+y^2}       &amp; \text{for } (x,y) \neq (0,0)   \end{cases} $$  Show that $f$ not differentiable at $(0,0)$ but all directional derivatives exist.  I don't know how to tackle this problem. Can someone give some hints or solve the problem? Thanks :) Fastest Square Root Algorithm What is the fastest algorithm for finding the square root of a number?  I created one that can find the square root of "$987654321$" to $16$ decimal places in just $20$ iterations   I've now tried Newton's method as well as my own method (Newtons code as seen below)  What is the fastest known algorithm for taking the second root of a number?  My code for Newton's Method (*Edit: there was an error in my code, it is fixed in the comments below):        a=2   //2nd root     b=97654321   //base     n=1   //initial guess     c=0   //current iteration (this is a changing variable)     r=500000   //total number of iterations to run     while (c&lt;r)      {         m = n-(((n^a)-b)/(a*b))  //Newton's algorithm         n=m         c++;         trace(m + "  &lt;--guess   ...   iteration--&gt;  " + c)     } Intermediate ring between a field and an algebraic extension. This is an exercise in some textbooks.     Let $E$ be an algebraic extension of $F$. Suppose $R$ is ring that contains $F$ and is contained in $E$. Prove that $R$ is a field.   The trouble is really with the inverse of $r$, where $r\in R$. How to prove that $r^{-1}\in R$, in apparent lack of a characterization of $R$.  It occurred to me to use the smallest field containing $R$ ($R$ is easily shown to be an integral domain), that's the field of quotients, and proving that it's $R$ itself, but I don't really know how to proceed.  A not-too-weak, not-too-strong hint will be much appreciated.   Beware $ $ Readers seeking only hints should  beware that there is now a complete answer. Using divisibility theorems, prove that if $\gcd(a,b)=1$ and $a|c$ and $b|c$, then $ab|c$.   This is pretty clear by UPF, but I'm having some trouble proving it using divisibility theorems. I was looking at , and if this could be proven, then the solution would follow immediately. How do I get the path of the directory in which a  script is located, inside that script? I want to use a Bash script as a launcher for another application. I want to change the working directory to the one where the Bash script is located, so I can operate on the files in that directory, like so: $ ./application My character has a bite attack from his race.  What happens if he gains another bite attack from class abilities or spells?  Does the damage increase?  Can he make more than one attack?  Or is it simply that only the better version applies?  I would prefer answers from a Pathfinder context but 3.5e is also acceptable. Why does correlation matrix need to be positive semi-definite and what does it mean to be or not to be positive semi-definite? I have been researching the meaning of positive semi-definite property of correlation or covariance matrices.   I am looking for any information on   Definition of positive semi-definiteness; Its important properties, practical implications; The consequence of having negative determinant, impact on multivariate analysis or simulation results etc. The add comment link and comment box overlaps bounty box What canon evidence is there that Stormtroopers are/are not still clones? Reading this article about , my nerd-rage started flaring as they claimed that Stormtroopers were still Fett-Clones 20 years after the rise of the Empire.  As I started thinking about it, I realized that everything I had read saying that Modern-Day Stormtroopers not being clones was from the EU - C Level books or games.   One of the quotes often cited for backing the idea that the Stormtroopers are clones comes from Princess Leia:     Aren't you a little short for a Stormtrooper?   But through the movie, paying close attention, Stormtroopers are often shown to be slightly different heights. One even hits his head in the doorway while others walk through uninjured.                                  Is there any G Canon fully canon (non-Legends/Infinities) evidence to support the idea that Stormtroopers are, or are not still clones at the time of Episode IV? Schengen visa. What qualifies as main destination? I'm planning a multi city trip soon. I'll be applying with the German embassy as I had planned on going to Berlin for 3 days before going to Prague, Vienna, and Budapest for 2-3 days each afterwards.   My question is, it is working out more conveniently for me to instead make Germany my last destination, rendering the first entry clause. And I can only apply with the German consulate as they are the only ones I can find an appointment for in time. Would staying in Germany for 4 days afterwards be enough to classify it as a main destination (as opposed to 2-3 days in the other cities)? I know this may be a tough or confusing question, but I have numerous existing materials I created and reuse for a project, which were all prepared for Blender Internal.  Now, I want to start the transition to Cycles, but I've hit a roadblock. How can I transition my materials without completely starting over? Or should I just forget it and start with fresh materials? How can I prevent installation of a specific package on Linux Mint? Why does the aorta spray blood when atmospheric pressure is higher than blood pressure? We are always introduced to magnets by pictures illustrating a parallepiped magnet, a horseshoe magnet, etc... Anyway the first time we actually calculate a magnetic field is for eelectromagnets. Indeed I've rarely seen explaining or calculating the magnetic field of a permanent magnet. I know formulas for the magnetic field of a moving charge, around a conductive wire, inside a solenoid, but I don't have idea on how to go about calcualting the filed of a simple permanent magnet. It's like that without the help of electricity I'm stuck. I'd guess it would be heavily dependent on the magnetic material, its shape and the medium in which is placed. I hope that someone would provide me some insights on why such formulas are  never introduced in most physics courses and lay down some examples of a permanent magnet field caluclation.