java.lang.NullPointerException at org.glassfish.hk2.classmodel.reflect.impl.TypesImpl.getType
java.lang.NullPointerException at org.glassfish.hk2.classmodel.reflect.impl.TypesImpl.getType
I'm using this code to get standard output from an external program:  &gt;&gt;&gt; from subprocess import * &gt;&gt;&gt; command_stdout = Popen(['ls', '-l'], stdout=PIPE).communicate()[0]   The communicate() method returns an array of bytes:  &gt;&gt;&gt; command_stdout b'total 0\n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file1\n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file2\n'   However, I'd like to work with the output as a normal Python string. So that I could print it like this:  &gt;&gt;&gt; print(command_stdout) -rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file1 -rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file2   I thought that's what the  method is for, but when I tried it, I got the same byte array again:  &gt;&gt;&gt; binascii.b2a_qp(command_stdout) b'total 0\n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file1\n-rw-rw-r-- 1 thomas thomas 0 Mar  3 07:03 file2\n'   How do I convert the bytes value back to string? I mean, using the "batteries" instead of doing it manually. And I'd like it to be OK with Python&nbsp;3. Role of capacitors in amplifier What is the significance of a coupling capacitor in a common-emitter amplifier? What would happen if it is removed? What will be  the effect on AC amplifier gain on removing it? If $A$ is compact, is then $f(A)$ compact? I am unable to understand what exactly is critical value.My question here is why do we fail to reject a null hypothesis when the test statistic is within the range of critical value.  What i am trying to ask is what is the property of the critical value that makes the hypothesized value to fall within the range implied by the critical value.  Thanks in advance "Switching" axes in 3d tikzpicture Overview  So say I want an arc between the x and z axis in the same way the following creates an arc between the x and y axis (MVCE):  \documentclass[border=5mm]{standalone} \usepackage{tikz} \begin{document}   \begin{tikzpicture}     \tikzset{       x={(0:1cm)},y={(50:0.7cm)},z={(90:1cm)}     }     \draw[-&gt;] (0,0,0) --++ (1,0,0) node[right]{$x$};     \draw[-&gt;] (0,0,0) --++ (0,1,0) node[right]{$y$};     \draw[-&gt;] (0,0,0) --++ (0,0,1) node[right]{$z$};     \draw (0,0,0) ++(0:.3) arc (0:90:.3);   \end{tikzpicture} \end{document}     One solution to this exact problem is to do scope and tell arc that the y-axis is the z-axis.      \begin{scope}       \tikzset{y=(90:1cm)}       \draw (0,0,0) ++(0:.3) arc (0:90:.3);     \end{scope}   The problem  However, I need this more generic since I don't necessarily know how the y-axis is defined, so I'm looking for a way to do, essentially this:      \begin{scope}       \switchYZAxes       \draw (0,0,0) ++(0:.3) arc (0:90:.3);     \end{scope}   or      \begin{scope}       \tikzset{y=\theZAxis}       \draw (0,0,0) ++(0:.3) arc (0:90:.3);     \end{scope}   The latter is problematic because it seems like I can't send polar coordinates to the \tikszet via a macro (which is the background for  question).  Any ideas? Thanks :) So here is one I wish to know:   I use Tri-Gate second effect, which allows me to target and banish one card on the field. Then I link that with another monster to bring out another link. Tri-Gate would be in the graveyard but then I use transcodes effect (1 of the 3 co-links) to bring it back from the graveyard.   Can I use the second effect again? Should initial e's after h-dropping be capitalized? A new Victorian-set British novel begins sentences containing h-dropping with lower-case e's, as in " 'e took my money, 'e did." This seems incorrect but I'm at a loss to find the rule. get values from ANY type Object How do I show that a two-qubit state is an entangled state? The Bell state $|\Phi^{+}\rangle = \frac{1}{\sqrt{2}}(|00\rangle + |11\rangle )$ is an entangled state. But why is that the case? How do I mathematically prove that? How do I access the list of currently logged on users through Terminal Services Manager in Windows Server 2012? I've already done a lot of searching (in particular: ) to try to prove this statement:      $f: A \to B$ is injective if and only if it has a left inverse. [I'm going to also assume $A$ and $B$ are nonempty.]   My attempt so far:     $\Leftarrow$ Suppose $f$ has a left inverse and $f(a_1) = f(a_2)$ for    $a_1, a_2 \in A$. Then there is a function $g: B \to A$ such that   $g\left(f(a_1)\right) = a_1$ and $g\left(f(a_2)\right) = a_2$. Since   $g$ is well-defined, it follows that $g\left(f(a_1)\right) =  g\left(f(a_2)\right)$, and hence $a_1 = a_2$.         $\Rightarrow$Now   suppose $f$ is injective. Then $f(a_1) = f(a_2) \implies a_1 = a_2$.   Furthermore, since $A$ is nonempty, there is an element $x \in A$.   Define $g: B \to A$ by  \begin{equation*} g(b) = \begin{cases}  f^{-1}(b), &amp; b \in \text{Im}(f) \\ x, &amp; b \in A \setminus  \text{Im}(f)\text{.} \end{cases} \end{equation*} This mapping is   well-defined, since if $f$ is injective, $f^{-1}(b)$ is unique.   My main question: does this imply that if $f: A \to B$ is injective that any mapping $g: \text{Im}(f) \to A$ is bijective? Otherwise, I don't understand why we can even use $f^{-1}$ on an element. [Please read the link above for more details - in proof 1.] How can you profile a Python script? I'm looking for the title of a short story by Ursula Le Guin about a scientist (?) who is given a drug that slows the timescale of his perception enormously, so that he can perceive that an alien (?) forest is actually behaving as a sentient being, reacting to current events, but at an enormously slow (from a normal human point of view) timescale. It might be in , but I don't remember the title (and it doesn't jump out at me from the list of titles) and don't have access to that collection right now. It is not &quot;The Word for World is Forest&quot;, nor &quot;Direction of the Road&quot; (from ), nor &quot;Vaster than Empires and More Slow&quot;, the latter two of which look at similar plant perception/time-scale issues. Update: it turns out that the description was right, but I had most of the details wrong: not Le Guin, not alien, not a scientist ... Given that   $x^x = y$; and  given some value for $y$   is there a way to expressly solve that equation for $x$? How to show that Klein four-group is a normal subgroup of the alternating group $A_4$ How do I monitor the computer's CPU, memory, and disk usage in Java? I would like to monitor the following system information in Java:   Current CPU usage** (percent) Available memory* (free/total) Available disk space (free/total)  *Note that I mean overall memory available to the whole system, not just the JVM.   I'm looking for a cross-platform solution (Linux, Mac, and Windows) that doesn't rely on my own code calling external programs or using JNI. Although these are viable options, I would prefer not to maintain OS-specific code myself if someone already has a better solution.  If there's a free library out there that does this in a reliable, cross-platform manner, that would be great (even if it makes external calls or uses native code itself).  Any suggestions are much appreciated.  To clarify, I would like to get the current CPU usage for the whole system, not just the Java process(es).  The SIGAR API provides all the functionality I'm looking for in one package, so it's the best answer to my question so far. However, due it being licensed under the GPL, I cannot use it for my original purpose (a closed source, commercial product). It's possible that Hyperic may license SIGAR for commercial use, but I haven't looked into it. For my GPL projects, I will definitely consider SIGAR in the future.  For my current needs, I'm leaning towards the following:   For CPU usage, OperatingSystemMXBean.getSystemLoadAverage() / OperatingSystemMXBean.getAvailableProcessors() (load average per cpu) For memory, OperatingSystemMXBean.getTotalPhysicalMemorySize() and OperatingSystemMXBean.getFreePhysicalMemorySize() For disk space, File.getTotalSpace() and File.getUsableSpace()   Limitations:  The getSystemLoadAverage() and disk space querying methods are only available under Java 6. Also, some JMX functionality may not be available to all platforms (i.e. it's been reported that getSystemLoadAverage() returns -1 on Windows).  Although originally licensed under GPL, it  to , which can generally be used for closed source, commercial products. Edits that shadow a suggested edit inconsistently reject but include the suggestion I have the edit privilege. If I edit a post which has a pending suggested edit, then:  My edit starts from the version resulting from the suggested edit. I'm not notified of that, or even of the existence of the suggested edit. (There's actually a clue, but it's easy to overlook — the edit summary field is pre-filled with the summary from the suggested edit.) The suggested edit is marked as rejected by Community with the message “This edit conflicted with a subsequent edit.” The suggester is not credited in the edit history, my revision combines the suggested edit with my modifications.  This can happen if an edit is suggested while I have the page open: I click on “edit”, and think I'm editing the version that I was just reading, but in fact I'm editing somebody's suggested edits. It also happens if I deliberately visit /posts/12345/edit, which . Examples: a  that I approved and then wanted to ; a  where I . There are two bugs here, but I'm making a single report because they're very closely linked.  I'm not told about the suggestion, so my edit includes content that I'm not aware of, yet is attributed to me. The suggestion is marked as rejected and the suggester is not credited in the edit history, yet the suggested changes are made. How can you tell when a sunset is going to be spectacular? I have a spot that I like to take sunset pictures. I find that the most spectacular moments last for only maybe 5-10 minutes. What I would like to do is know about a half hour before that a sunset is going to be spectacular, so I can grab my camera, tripod, walk 5-10 minutes to my sunset spot, set up, and have a few minutes to spare in case something happens. However, I've often missed really cool sunsets, because I just don't know when to photograph them. How can you tell beforehand when a sunset is going to be spectacular? Thanks! Can I configure bash to execute "clear" before every command typed in the console? I would like to configure bash to execute clear command every time I type some command in the terminal (before executing my command). How can I do that?  I'm using Debian Linux. Suppose $X$ is a finite set and $f : X \to X$ is a function. Then $f$ is injective if and only if $f$ is surjective. Suppose $X$ is a set and $f : X \to X$ is a function.  If $X$ is a finite set, prove that $f$ is injective if and only if $f$ is surjective. Show that when $X$ is an infinite set, the statement is not true in general.   For that, let $X = \mathbb{R}$ and find a function $f: \mathbb{R} \to \mathbb{R}$ which is injective but not surjective, and a function $g: \mathbb{R} \to \mathbb{R}$ which is surjective but not injective  My attempt at the first part   Suppose that the function is surjective but not injective. Let $a,b \in X$ such that $f(a)=f(b)$ but $a \not =b$. Now since this is a finite set mapping to itself then there are not enough elements in $X$ to map to $X$ since two elements were used to map to one element, thus the function can't be surjective. Therefore if the function is surjective it is also injective.   Now suppose that the function is injective but not surjective. Let $a \in X$ such that $f(b)\not =a$ for all $b \in X$. Since the function was assusmed to be injective each $a \in X$ must map to an element of $X$, thus must have two elemetns in $X$ mapping to the same element in $X$. Hence the function can't be injective, therefore if the function is injective it must be surjective.   Would an exponetial function work for injective but not surjective since can't map to negative numbers. And an example of a function that is surjective but not injective could be a log function since none of the negative numbers get mapped to anything?   Also I'm having trouble seeing why it has to be finite for the first part to work. I understand it has something to do with the pigeonhole principle but its not that clear to me.