I must write a class Person with 3 attributes (Name,Surname,Age) in all his instances. How can i set it that it cant be possible to add more attributes? class Person:    def __init__(self,name,surname,age):         self.name=name         self.surname=surname         self.age=age
What is the purpose of  in Python — especially with respect to when I would want to use it, and when not?
Prove that there exists irrational numbers $x$ and $y$ such that $x + y$ is rational, without using subtraction My homework has this problem:     Prove that there exist irrational numbers $x$ and $y$ such that $x +  y$ is rational.   There is an easy solution that I found on mathbitsnotebook.com:     \begin{align} \left(2+6\sqrt{7}\right) + \left(-6\sqrt{7}\right) = 2.\end{align}   Can we prove the same without using subtraction? Where does the curve $x^y = y^x$ intersect itself? This problem is quite easily solved by using logarithms and derivative and forming the function $f(x,y) = x^y - y^x$, however there are assertions that this problem can be solved without using either of the two. I can not see how one would proceed to solve this problem in the absence of logarithmic manipulation and differentiation. Can anyone shed some light on this? Reading the book on which I'm learning English, I've come across a weird (for me) omitting the "to" in sentence: "I'd better go meet with him then."  Say, if it were "I'd better go to meet with him then.", would there be any difference between the two sentences? When I should prefer using one instead the other?  P.S. Sorry for my bad English. If I made a mistake somewhere, please correct me. Let $(a_n)_{n≥0}$ and $(b_n)_{n≥0}$ be two sequences of a nomed algebra such that $\sum{\| a_n\|}$ and $\sum{\| b_n\|}$ converge, and$ $$$\forall n, \  a_n, b_n \neq 0$$  Show that $(\forall  k \in \mathbb N^*,  \ \sum_{n=0}^{\infty}{a_n}^k = \sum_{n=0}^{\infty}{b_n}^k) \implies \exists\ \sigma \in{\mathfrak S}_{\mathbb N} \ ,\ (a_n) = (b_{\sigma(n)})$  The vector-space should be a finite-dimensional $\mathbb R$-vector-space.   I do not see how to deal with the hypothesis. If you have ideas/hints...  It would be relevant to deal with complex sequences even if it is less general. But I don't think one can generalize using real and complex cases. Expectation of random variables ratio Are there any rules relevant to involuntary movement and effects other than Opportunity Attacks? PHB p. 195 states that involuntary movement does not provoke :     You also don't provoke an opportunity attack when you teleport or when someone or something moves you without using your movement, action, or reaction.   Is there a general rule somewhere about involuntary movement and how it interacts with other effects?  The question arose at our table about what happens if a creature is dragged via the Thorn Whip spell across an area of Spike Growth.  Does the involuntarily moving creature take the damage from the spikes as if he'd voluntarily moved through them?    Logically, yes, if you're being dragged through spikes, you take damage from them as if you'd walked through them. But logically, if I drag you past my ally, my ally would be able to make an Opportunity Attack, likely more easily than if you were moving under your own power.  Presumably that is not allowed for balance reasons rather than versimilitude reasons, so I wonder if the same should apply to other effects? Help, I cannot get my test code coverage higher than 75%! Code below When I boot Ubuntu 10.04.3 from a live CD, it asks me to enter a username and password. I have not booted before, and I haven't created an account. Great Theorem - Help name the Sci-fi book read long ago I'm trying to find a book I read long back. This book may have won a Hugo/Nebula (Trust me I've googled to death this one!).  Don't remember much of the story (that's why I want to re-read it). What I remember is that some of the powers in the book are called "Gods". And they have brains the size of the planets (or planets being their brains).  The protagonist in the climax, solves a theorem (The Great Theorem, perhaps) by remembering one of the obscure theorems (Jacuzi (?)) and incorporating it. This [Great] theorem helps spaceships helps find the shortest route from point A to B. He surprises the antagonist by reaching the vantage point quickly with the help of his new knowledge, and blasts his enemy's spaceship.  The ending of the book - as I remember it is - that the protagonist wants to become a God himself.  Please let me know the title &amp; author of this book if you've read it.  PS #1:  BTW, It's not Asimov's The Gods Themselves :) PS #2:  It's published at the least before 1998 Temporal Table that doesn't use system time We want to implement temporal tables in SQL Server 2016. We are creating a Datawarehouse and developing Type 2 Slowly changing Dimension Tables.  For the BeginDate, we want it to be dependent on transaction date and not the current getdate time. We are reprocessing a history of transactions. Example below, customer has gym or bank status, and goes from inactive, to active, or pending, dependent on transaction date.  We currently have this.  CREATE TABLE dbo.Department (     CustomerId int primary key,     MembershipStatus int,     TransactionDate datetime  );   We we would like to create a table like this.  CREATE TABLE dbo.DepartmentHistory (     CustomerId int primary key,     MembershipStatus int,     TransactionDate datetime,     BeginDatetime datetime,     EndDatettime datetime  );   Example usage would be:   first Customer Transaction on 3/5/2018 as Pending P        +------------+--------+-----------+---------+     | CustomerId | Status | BeginDate | EndDate |     +------------+--------+-----------+---------+     | 1          | P      | 3/5/2018  | NULL    |     +------------+--------+-----------+---------+    second transaction is 4/21/2018 is Active A        +------------+--------+-----------+-----------+     | CustomerId | Status | BeginDate | EndDate   |     +------------+--------+-----------+-----------+     | 1          | P      | 3/5/2018  | 4/21/2018 |     | 1          | A      | 4/21/2018 | NULL      |     +------------+--------+-----------+-----------+ Prove the definitions of $e$ to be equivalent How to prove that the following definitions of $e^x$ are equivalent, with as simple tools as possible and without any knowledge of $e$ or logarithms ?  $$\sum_{n=0}^{\infty} \frac{x^n}{n!}=\lim_{n\to\infty}\left(1+\frac{x}{n}\right)^n$$  Also preferably, prove that this is $a^x$ for some real number $a&gt;0$. Is there any way (such as a command or environmental variable) to determine what window manager is the one actively running in the current session? Complex Collision Boxes I'm trying to get a ball to go through in between the cup gear things shown in the screenshot below.   It seems that the collision box does not consider the cups. Yes, the ball fits and they are rotating in the right direction.  If there is already an answer to this, please link it.       If you have any questions about what is going on/ what the project is, feel free to ask. Traveling with visa in my old passport My old passport in which an ECR was stamped,with passport expiry date in 2017.I got a Dubai visit visa on its passport number but later on as I was told that it'l be a problem for me to travel to Dubai so I got a new passport re-issued with ECNR with a new passport number.  So will it be a problem for me to travel or do I have to get my UAE visit visa details of my old passport number change to my new passport number? This user is only displaying 56 rep.   But surely (s)he has much more than that.        The user has also never given out any bounties.  Also, badges are missing: I want to install selenium webdriver in my Ubuntu 16.04 system for python For the finite-dimensional case, we have a canonical isomorphism between $\mathbf{V}$, a vector space with the usual addition and scalar multiplication, and $(\mathbf{V}^*)^*$, the "dual of the dual of $\mathbf{V}$." This canonical isomorphism means that the isomorphism is always the same, independent of additional choices.   We can define a map $I : \mathbf{V} \to (\mathbf{V}^*)^*$ by $$x \mapsto I(x) \in (\mathbf{V}^*)^* \ \text{ where } \ I(x)(f) = f(x) \ \text{for any } \  f \in \mathbf{V}^*$$  My Question: what can go wrong in the infinite-dimensional case? The notes I am studying remark that if $\mathbf{V}$ is finite-dimensional, then $I$ is an isomorphism, but in the infinite-dimensional case we can go wrong? How? For any triangle with sides $a$, $b$, $c$, show that $a^2b(a-b)+b^2c(b-c)+c^2a(c-a)\ge 0$ For any triangle with sides $a$, $b$, $c$, prove the inequality $$a^2b(a-b)+b^2c(b-c)+c^2a(c-a)\ge 0 .$$   This is IMO 1983 problem 6.  I tried substituting $a=x+y$, $b=y+z$, $c=z+x$ but well it doesn't help in any sense except wasting 3 pages that lead to nothing (please don't mind the joke). Using $a=2R\sin A$, $b=2R\sin B$, $c=2R\sin C$ also didn't lead to anything for me. Could you give me a hint for finding the proper substitution? What ensures big holes in my bread? What is polarisation, spin, helicity, chirality and parity? Polarisation, spin, helicity, chirality and parity keep confusing me. They seem to be related, but exactly how they are related is unclear to me. Can someone maybe give a short overview about what these quantities mean and how they are related? What are the values for e.g. basic particles like electron or photon?