Say I have      x = [[0,0]]     y = x[-1]   Then why does      y[1] += 1   give       x = [[0,1]]     y = [0,1]    That is, I'm confused as to why it also changes what x is, even though I only specified something to do with y?
I needed to create a list of lists in Python, so I typed the following: my_list = [[1] * 4] * 3  The list looked like this: [[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]]    Then I changed one of the innermost values: my_list[0][0] = 5  Now my list looks like this: [[5, 1, 1, 1], [5, 1, 1, 1], [5, 1, 1, 1]]    which is not what I wanted or expected. Can someone please explain what's going on, and how to get around it?
JDBC-ODBC Bridge queries to Access fail when they have accented characters Can a countable set contain uncountably many infinite subsets such that the intersection of any two such distinct subsets is finite? Can't disable windows 10 PIN complexity I recently linked my Microsoft Office account to my school to have access to Office for students. Right after linking my account, I couldn't login to my computer again with my 4-digit pin code and got the message: "your organization has set the following pin code requirements. Your pincode has to be at least 6 digits long."   I had to change my pincode but I want to change it back to my original 4-digit one. Some internet research has made me enable gpedit.msc, but when I try to find the PIN complexity setting in gpedit (Computer Configuration\Administrative Templates\System\PIN Complexity) it just isnt't there.   Another possible path in gpedit I found on the internet to do this was: Computer Configuration > Administrative Templates > Windows Components > Windows Hello for Business > PIN Complexity, but that also didn't work as I don't have "Windows Hello for Business"   I also tried resetting my computer to the date before I joined my 'organization', but that didn't work either.   Does anyone have an idea how I can resolve this issue? I am writing a bash script to look for a file if it doesn't exist then create it and append this to it:  Host localhost     ForwardAgent yes   So "line then new line 'tab' then text" I think its a sensitive format.  I know you can do this:  cat temp.txt &gt;&gt; data.txt   But it seems weird since its two lines. Is there a way to append that in this format:  echo "hello" &gt;&gt; greetings.txt Centos recently updated to 7.3 and there's been problems with sshd sftp group permissions. I have one user that is chrooted to it's home directory, and that user is in group sftponly. Then i have the /var/www directory, which has 775 permissions and owner is apache and owner group is sftponly. I have a bind link pointing from /home/user/files/web --> /var/www, so the user can access /var/www even though being chrooted to it's home directory. I can view files in /var/www with that user, but impossible to edit or add anything. This worked fine before the big Centos 7.3 update, and now it's stopped working. Any ideas? How to create dynamic JSF form fields Is there a way to view Google Chrome browsing history past three months ago? I'm trying to find a page I looked at months ago but it looks like it's disappeared off the face of the planet. I thought I would have better luck looking through my Google Chrome browsing history, but I can't see history past September. Can I force Google Chrome to display history further into the past? Can I retrieve the history manually from a directory? Is the history data gone? How to install and configure Wine? I am looking for a step by step instruction to guide me in the ways of installing, configuring and debugging many of the issues new users have when dealing with Wine in Ubuntu.  What is the recommended way of installing Wine, some of the key issues that it has and how to solve them?  If I have a specific problem with an App in Wine, how do I go about solving it? What are the recommended steps to ensure that I can fix a problem related to an app I wish to use? Variables in batch file not being set when inside IF? I have two examples of very simple batch files:  Assigning a value to a variable:  @echo off set FOO=1 echo FOO: %FOO% pause echo on   Which, as expected, results in:  FOO: 1  Press any key to continue . . .   However, if I place the same two lines inside an IF NOT DEFINED block:  @echo off IF NOT DEFINED BAR (     set FOO=1     echo FOO: %FOO% ) pause echo on   This unexpectedly results in:  FOO:  Press any key to continue . . .   This shouldn't have anything to do with the IF, clearly the block is being executed.  If I define BAR above the if, only the text from the PAUSE command is displayed, as expected.    What gives?    Follow up question: Is there any way to enable delayed expansion without setlocal?   If I were to call this simple example batch file from inside another, the example sets FOO, but only LOCALLY.   For example:   testcaller.bat   @call test.bat  @echo FOO: %FOO%  @pause    test.bat   @setlocal EnableDelayedExpansion  @IF NOT DEFINED BAR (      @set FOO=1      @echo FOO: !FOO!  )    This displays:   FOO: 1  FOO:  Press any key to continue . . .    In this case, it appears that I have to enable delayed expansion in the CALLER, which may be a hassle. Original  The remainder provided by polynom.sty is NOT complete (as shown in the following figure).      My Objective  When I was in senior high school, my teacher made the diagram like below. :-)  Thus the final step must show the TOTAL remainder and mark it with L-shaped curve.  NOTE  I am sorry. The previous post I forgot to put back -1/4 in the original position. It have made you confused. Now there is no mistake anymore. :-)      Minimal Code  \documentclass{article} \usepackage{polynom,array} \usepackage[table]{xcolor}   \makeatletter \def\pld@ArrangeResult#1{%     \ifx\pld@remainder\@empty         \@tempcnta\pld@maxcol\relax         \pld@InsertItems@do\pld@lastline             {\pld@firsttrue\pld@PLD{\pld@R{0}{1}}}%     \fi     \ifnum\pld@currstage&gt;\z@         \pld@Extend\pld@allines{\pld@lastline\cr}%     \else         \pld@InsertFake\pld@lastline     \fi     \pld@iftopresult         \def\pld@lastline{\pld@PrintPoly\pld@divisor%         %====================================================================================         \quad\smash{{\color{red}\rule[-6pt]{\arrayrulewidth}{17pt}}}\kern-\arrayrulewidth&amp;}%         %====================================================================================     \else         \let\pld@lastline\@empty         \ifx B\pld@style\else             \def\pld@lastline{\pld@leftdelim\strut\pld@rightxdelim&amp;}%         \fi     \fi     \expandafter\pld@AR@col\expandafter\pld@PLD                            \expandafter\pld@lastline#1+\relax+%     \pld@SplitQuotient     \pld@iftopresult         \let\pld@currentline\@empty         \expandafter\pld@AR@col\expandafter\pld@PLD                                \expandafter\pld@currentline                                            \pld@quotient+\relax+%         \expandafter\pld@AR@col\expandafter\pld@XPLD                                \expandafter\pld@currentline                                            \pld@shadow+\relax+%         \edef\pld@subline{%             \noexpand\cline{\tw@-\pld@maxcol}%             \noalign{\vskip\jot}}%         \pld@Extend\pld@currentline{\expandafter\cr\pld@subline}%     \else         \@tempcnta-\@tempcnta         \advance\@tempcnta\pld@maxcol\relax \advance\@tempcnta\@ne         \edef\pld@span{\the\@tempcnta}%         \ifx B\pld@style           \pld@AddTo\pld@lastline{%             &amp;\multispan\pld@span${}=%             \pld@PrintPolyWithDelims\pld@divisor             \expandafter\pld@IfSum\expandafter{\pld@divisor}{}{\cdot}%             \expandafter\pld@IfSum\expandafter{\pld@quotient}\pld@true                                                              \pld@false             \pld@if \pld@leftdelim                     \pld@PrintPolyShadow                     \pld@rightdelim               \else \pld@PrintPolyShadow \fi             \pld@firstfalse             \expandafter\pld@PrintRemain\expandafter{\pld@remainder}$}%         \else           \pld@AddTo\pld@lastline{%             &amp;\multispan\pld@span$\pld@leftxdelim\strut\pld@rightdelim             \pld@div             \pld@PrintPolyWithDelims\pld@divisor=             \pld@PrintPolyShadow             \ifx\pld@remainder\@empty\else                 +{}%                 \setbox\z@=\hbox{$\displaystyle                   \frac{\let\strut\@empty\pld@firsttrue \expandafter                         \pld@PrintRemain\expandafter{\pld@remainder}}%                        {\let\strut\@empty\pld@PrintPoly\pld@divisor}$}%                 \dp\z@=\z@\box\z@             \fi             $}%         \fi     \fi \expandafter\pld@AR@\pld@allines\relax} \makeatother   \arrayrulecolor{red} \arrayrulewidth=0.8pt \def\strut{\rule[-6pt]{0pt}{12pt}}  \begin{document} \polylongdiv[style=A]{\frac{3}{7}x^9+x^2-\frac{1}{4}}{\frac{9}{5}x^4-1}  \vspace{1cm} \polylongdiv[style=A]{x^4-1}{x^2-1} \end{document} What is a subnet mask, and the difference between a subnet mask of 255.255.255.0 and 255.0.0.0? My DSL/WiFi router provided by my ISP has an internal IP address of 10.0.0.138, the addresses provided by DHCP are in the format of 10.0.0.xxx.  Now, I want to start using static IP addresses on my local network, and I don't know what to provide for the subnet mask.  What is a subnet mask?  Should I be using 255.255.255.0 or 255.0.0.0 as my subnet mask? What is the difference? Can I use the Twig template engine? I do a lot of  development and I like their templating language. , the , looks very much like it.  How can I use Twig in Drupal 7 or even Drupal 6? Invite people who liked my first page to like another one in Facebook Are the groups $\mathbb{C}$ and $\mathbb{R}$ isomorphic? Services Actions Missing in Central Admin How to escape text for regular expression in Java Is there any API function for shutting down Windows while installing any pending updates? Can't mount an IDE HDD - "can't read superblock" error message I'm trying to mount my HDD,  /dev/sdb, which is connected via an enclosure but every time I try do so I get an error message   mount: /dev/sdb: can't read superblock   How do I solve this problem and mount my HDD? Why doesn't Stack Apps have its own meta? I just realized I can't unrar .rar files on my Ubuntu machine!  What's the easiest way to accomplish this fundamental task? If possible I'd love something like 7Zip that I can just right Click, and extract and have the program worry about how to do it regardless if it's a .zip, a .rar or a .foo compressed file.