I have experienced some problem by using a nested list in Python in the code shown bleow.  Basically, I have a 2D list contains all 0 values, I want to update the list value in a loop.  However, Python does not produce the result I want. Is there something that I misunderstand about range() and Python list indices?  some_list = 4 * [(4 * [0])] for i in range(3):     for j in range(3):         some_list[i+1][j+1] = 1 for i in range(4):     print(some_list[i])   The results I expected are:  [0, 0, 0, 0] [0, 1, 1, 1] [0, 1, 1, 1] [0, 1, 1, 1]   But the actual results from Python are:  [0, 1, 1, 1] [0, 1, 1, 1] [0, 1, 1, 1] [0, 1, 1, 1]   What's going on here?
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?
I want to describe the variables involved in an equation in an itemized environment such that every item begins with the variable name and subsequently comes the description for it. I'd like to have all the descriptions left aligned.  Here is a MWE that of course does not produce what I am looking for.  \documentclass{standalone} \begin{document} $E[g(x)] = \int_{-\infty}^{+\infty} f_X(x) \, g(x) \, \mathrm{d}x$. % where, % \begin{itemize}     \item $x$      \quad is a continuous random variable.     \item $f_X(x)$ \quad is the PDF of $x$.     \item $g(x)$   \quad is a function of $x$. \end{itemize} \end{document} Values of $\sum_{n=0}^\infty x^n$ and $\sum_{n=0}^N x^n$ Why does the following hold:  \begin{equation*} \displaystyle \sum\limits_{n=0}^{\infty} 0.7^n=\frac{1}{1-0.7} = 10/3\quad ? \end{equation*}  Can we generalize the above to      $\displaystyle \sum_{n=0}^{\infty} x^n = \frac{1}{1-x}$ ?   Are there some values of $x$ for which the above formula is invalid?  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This leaves a blocked User Interface until the render finishes, meaning that you can't cancel the process, except by killing Blender. The problem is that the render may be too big in resolution, and the user could want to stop the process when realizing that the render could take hours, so the idea is to cancel this process without losing the currently opened project.  If I call,  bpy.ops.render.render("INVOKE_DEFAULT")   I get a nice preview bar in the Info Window with a clickable "X" button. I want the user to be able to press that button to cancel the operation if needed, but for a series of renders (not animation).  The problem here seems to be when trying to loop this command with the INVOKE_DEFAULT context to write several renders. I made a lot of testing, and this way of calling the render operator seems to continue with whatever is next in the script, so it loops very fast and ends before the rendering actually finishes.  I think that I need some way to stop the script and make it wait until render finishes to continue looping with the next ones. I tried the "render_complete" and "render_cancel" handlers, but I can't use them to start a new render or even make the rest of the script wait until the loop of renders is complete. I tried threading and events without success either. Maybe I'm doing something wrong.  import bpy  render = bpy.context.scene.render path = render.filepath = "/tmp/" shots = ["one", "two", "three"]  for x in shots:     render.filepath = path + x     bpy.ops.render.render("INVOKE_DEFAULT", write_still=True) # this doesn't work      # but if I use:     # bpy.ops.render.render(write_still=True)     # without the INVOKE thing, images are written as expected,     # but losing the possibility to see the progress and cancel rendering What is the best way to get the names of all of the tables in a specific database on SQL Server? Is it possible to run Android apps on Ubuntu? And I don't mean inside an emulator, but natively, as you would with any other application installed using the Ubuntu Software Center. Bash: command not found Fermi's golden rule and infinite probablity? I am slightly confused about the application of . Which during standard derivations indicates a probability of transitioning from the state $|i \rangle$ to the state $|f\rangle$ of: $$P=\frac{2\pi t}{\hbar^2} | \langle f | \hat V | i \rangle|^2 \delta(E_f-E_i-\hbar \omega)$$ This holds for large values of $t$ but for arbitrarily large values of $t$: $$P&gt;1$$ Which (to me anyway) makes no physical sense since there can't be a probability greater then 1 of been in the final state. If my interpretation is right then how is this problem resolved/allowable? and if it is wrong what part of what I have said is wrong? What do two question marks together mean in C#? Ran across this line of code:  FormsAuth = formsAuth ?? new FormsAuthenticationWrapper();   What do the two question marks mean, is it some kind of ternary operator? It's hard to look up in Google. What is reflection and why is it useful? What is reflection, and why is it useful?  I'm particularly interested in Java, but I assume the principles are the same in any language. Is the unit sphere in $\Bbb R^4$ path connected? How can I keep multiple live/bootable ISO images on a single USB drive? Unupvote immediately followed by an upvote gives me a net -10 reputation points I want to have an index entry typeset as $a_\text{T}$, so I issue the command \index{at@$a_\text{T}$}. Each use of this index command creates a separate line in the index. How can I get \makeindex to recognize they all reference the same topic?  My index entries look like this: $ is not a function in drupal 7 theme Can I use a charger with more output amperage than the device needs? Is there proof that the DSA construction, also used by ECDSA, is secure assuming that discrete logarithms in the relevant group representation are difficult? Retrieve globalpicklist/globalvalueset without SOQL Is it possible to retrieve the values of a Global Picklist/GlobalValueSet using Schema class without a SOQL ? Show if a user is online, idle, or offline on their account page? I want to display the status of the user on the account page. I added the following code in the theme I am using. It works, but users are never displayed offline. Why? What is wrong in the code? user.html.twig &lt;div class=&quot;bs-field-status&quot;&gt;   {% if status == 'Online' %}     &lt;i class=&quot;user-online fa fa-circle fa-lg&quot;&gt;&lt;/i&gt; Online   {% elseif status == 'Absent' %}     &lt;i class=&quot;user-absent fa fa-circle fa-lg&quot;&gt;&lt;/i&gt; Absent   {% else %}     &lt;i class=&quot;user-offline fa fa-circle fa-lg&quot;&gt;&lt;/i&gt; Offline   {% endif %} &lt;/div&gt;  bootstrap_subtheme_front_office.theme &lt;?php /**  * @file  * Bootstrap sub-theme.  *  * Place your custom PHP code in this file.  */  use Drupal\Core\Database\Database;  /**  * Implements hook_entity_presave().  */ function bootstrap_subtheme_front_office_preprocess_user(&amp;$variables) {   // get user object   $user = $variables['elements']['#user'];   //- The user has logged in at least once   if ($user-&gt;getLastLoginTime()) {     if (account_is_logged_in_less_then_thirty_minutes($user-&gt;id())) {       $status = 'Online';     }     else {       $status = 'Absent';     }   }   else {     $status = 'Offline';   }   $variables['status'] = $status; }  /**  * @param $uid  *  * @return bool  */ function account_is_logged_in_less_then_thirty_minutes($uid) {   $connection = Database::getConnection();   $query = $connection-&gt;select('sessions', 'sessions')     -&gt;fields('sessions', ['sid', 'uid', 'timestamp'])     -&gt;condition('sessions.uid', $uid, '=')     //- chef if the user was online in 30 minutes (60 * 30)     -&gt;condition('sessions.timestamp', \Drupal::time()         -&gt;getRequestTime() - (60 * 30), '&gt;')     -&gt;execute();   //- Get result.   $results = $query-&gt;fetchAll(\PDO::FETCH_OBJ);   return (count($results) &gt; 0) ? TRUE : FALSE; }