For some tox tests, I need a Python 3.5 interpreter. How can I install it on Ubuntu 18.04?
How can I install a different version of Python using apt-get?  Obviously I realise I can install using the source tar ball, however I would prefer not to install from source and instead use the package manager, as that's what it's there for. Surely somewhere reputable builds .deb files for the latest Python releases (why python.org don't is beyond me) that I can reference.   What do I need to do to reference them and what issues might it create when upgrading to the next version?  If there is no way except for building from source, is there a (pseudo) package that I can can install that will provide all of the dependencies needed without having to find and install each individually? So that I don't get:  The necessary bits to build these optional modules were not found: _bz2                  _curses               _curses_panel       _dbm                  _gdbm                 _lzma               _sqlite3              _ssl                  _tkinter            readline              zlib
The following is exercise 8.2 in 3rd edition (and exercise 8.19 in 2nd edition) of Goldstein's Classical Mechanics.   Adding the total time derivative of a function of $q_i$ and t to the Lagrangian will not change the the Euler-Lagrangian equation. So if we make the following change to Lagrangian,   $$L'(q,\dot{q},t) = L(q,\dot{q},t) + \frac{dF(q_1,q_2,...,q_n,t)}{dt}$$ we can get  $$ \frac{d}{dt}\frac{\partial{L'}}{\partial{\dot{q_i}}} - \frac{\partial{L'}}{\partial{q_i}} = 0 $$ from  $$ \frac{d}{dt}\frac{\partial{L}}{\partial{\dot{q_i}}} - \frac{\partial{L}}{\partial{q_i}} = 0 $$  How can we get the corresponding Hamiltonian equation part? This is to prove  $$ \dot{p'_i} = \frac{\partial{H'}}{\partial q_i} $$ $$ -\dot{q_i} = \frac{\partial{H'}}{\partial p'_i}  $$  from   $$ \dot{p_i} = \frac{\partial{H}}{\partial q_i} $$ $$ -\dot{q_i} = \frac{\partial{H}}{\partial p_i}  $$ where $p'_i = \frac{\partial L'}{\partial \dot q_i}$.  Edit  The corresponding $H'$ is $$ H' = \sum_k{p'_k \dot{q_k}} - L' $$ where $p'_k = \frac{\partial L'}{\partial \dot q_k}$. What free/open source image design programs can you recommend? Are there any free/ open source image designing programs that you can recommend? Adverb sentence query Determine if a set of tiles on a grid forms an enclosed shape How can I get around giving my mobile phone number to Google? When I want to register an account with Gmail now, it says "Google will send a text message containing a verification code to your mobile phone."  I don't want to give Google my mobile phone number!!  How do I get around this? What is a good word to describe someone who is empathetic, quick, and witty in conversation Travelling as an unmarried Western couple in Indonesia When entering the US on an international flight, and then on to a connecting domestic flight, what is the exact order of the process that will take place? In other words, what happens first, second, third, etc.? Overleaf does not compile after using Biblatex In electrostatics, why the electric field inside a conductor is zero? In electromagnetism books, such as Griffiths or the like, when they talk about the properties of conductors in case of electrostatics they say that the electric field inside a conductor is zero.  I have 2 questions:    We know that conductors (metallic) have free electrons which randomly moves in all directions, so how come we can talk about electrostatics which by definition means stationary charges? When the textbooks try to show why the electric field inside a conductor is zero they say let us put our conductor in an electric field. What happens then is that there will be an induced surface charge density which consequently induces an electric field within the conductor such that the total electric field within the conductor will be zero. That is perfectly understood, but my problem is the following: the original claim was that the electric field within a conductor is 0, not the electric field after putting the conductor in an external electric field it became zero. I do not understand the logic! How is the minimum of a set of IID random variables distributed? If $X_1, ..., X_n$ are independent identically-distributed random variables, what can be said about the distribution of $\min(X_1, ..., X_n)$ in general? I have a PHP script that can encode a PNG image to a Base64 string.  I'd like to do the same thing using JavaScript. I know how to open files, but I'm not sure how to do the encoding. I'm not used to working with binary data. When to use ''[verb] that'' I would like to know when to say think(s) that, say(s) that and mean(s) that and when to omit that. Can't watch youtube videos with chromium on ubuntu 13.04 64-bit I've digged all over google but I can't find any solution to my problem.   Firefox works pretty well. I have this issue only with chromium and only with youtube. I have no problem watching videos at any other site with chromium.   When I try to watch a video a black screen occurs and after a while it gives me the warning "an error occurred". Weirdly, sometimes when I try a couple of refreshing it starts to play but then the issue occurs again.  I tried removing-reinstalling chromium or the flash plugin but it did not do any good. Do muggleborns get their letter on their 11th birthday or the summer before they start Hogwarts? A lot of the fanfiction seems to like to give Hermione her letter in September to coincide with her birthday. That just doesn't seem very logical for the Statute of Secrecy, as you then have 10 out of every 12 10-year-old wizards and witches knowing about magic while finishing the school year (assuming even distribution of birthdays).   It seems to me that this is just asking at least one of them to brag about knowing magic and spill the secret.   Also this would mean that the poor kid born on 30 of August would only have 2 days to adjust to being magical before being shepherded off to a boarding school in the middle of nowhere.  From another point of view, getting such news on your birthday can screw up a lot of celebration plans.  Also, from rereading the memory from Dumbledore where he introduced magic to Tom, there is no mention of snow or even closeness to his birthday from the caretaker.  I believe this view came from the fact that Harry got his letter on his birthday but that piece of fanon seems to forget that letters were being sent up to at least a week or 2 beforehand (leading to the Dursleys hiding on a rock in the sea in the first place). I'm moving all files to a new computer, via an external hard drive. I am certain that broken links will be a concern. What can I do to fix this? Is there a 'Best Practices' kind of way to prevent this problem beforehand? I have many hundreds of .blend files, and of course, I fear losing them. What's the best way to generate a tag cloud from an array using h1 through h6 for sizing? I had just arrived at the hotel, checked in and gotten into my room. Just as I was about to unpack, I noticed that one of my bags was missing. At first I thought I had left it back at the airport, but it turned out that I had left it on the taxi.  Here, what's the meaning and role of "just"?  Why do you guys input the word "just" here?  What exactly does the word do grammatically?   Could you help me? Using fflush(stdin) I know that a perpetual motion machine (a device that produces work without an energy source) would violate several physical laws, the first that comes to mind being the . I also understand that a claim that perpetual motion is possible would probably not be congruent with the scientific method, occum's razor, etc.  What I am interested in is whether there exists some logical and intuitively meaningful (to they lay person) demonstration that perpetual motion is universally impossible, based only on axioms rooted in observable physical phenomena, rather than the obvious reasons why it is merely improbable and incompatible with some of our physical laws.  Certain violations of physical laws, such as travelling faster than the speed of light, can be shown to be unlikely as they would cause paradoxes or logical impossibilities, such as a . In that instance, the axioms needed to establish a paradox (time dilation) are empirically observable, and a counter-claim would require the existence of new paradox-resolving laws that are not established, or the permission of paradoxes which is difficult to imagine.  Conversely, the idea that some invention is impossible on the basis of its violation of a physical law alone is difficult because it requires a .  So, without relying on the assertion that a physical law is omnipresent (e.g. conservation of energy), is there some impossibility or logical paradox that would arise from the existence of a machine that could produce work without indefinitely without an energy source?  Finally, I'm very aware that perpetual motion is a bit of a dirty word and will likely touch a nerve with people, so please take the time to let me know how I can make this question less offensive and avoid the inevitable down-votes.