Python Iterate Through List of Lists of Objects and Call a Method
List of lists changes reflected across sublists unexpectedly
If you go to  and are a 4k+ user on Anime.SE, you will see the following:        There is one reopen vote on this question, but the reopen vote count is displayed on a different line than the word "reopen". This is slightly silly, and would perhaps benefit from converting reopen (1) to reopen&amp;nbsp;(1), and likewise for close and delete votes. (Or any other way of preventing a line break between the vote type and the vote count.)  A repro (the close link) from here on Meta: Conjugating verbs for nouns referring to groups of people Possible Duplicate:          Frequently when reading tech articles, I see sentences like "Microsoft have released ..." or "Apple have announced ...". This seems wrong to me because the nouns are singular; Microsoft and Apple are individual companies, even though they refer to groups of people. I have not seen this usage outside of tech journalism, but it's pervasive enough that it makes me wonder: is this actually the correct usage?  As a follow-up question, is it correct to use a plural pronoun for a singular antecedent like this? For example, "Apple has announced they are changing their name to Orange" or "Apple has announced it is changing its name to Orange". The second form seems technically correct but sounds awkward. Homology of $S^1 \times (S^1 \vee S^1)$ I'm trying to solve question 2.2.9(b) in Hatcher's Algebraic Topology.   Question: Calculate the homology groups of $X=S^1 \times (S^1 \vee S^1)$.  My attempt: I try to use the Mayer-Vietoris sequence.   Let $A=S^1 \times (S^1 \vee \text{small bit}) =S^1\times S^1$ and $B=S^1 \times ( \text{small bit} \vee S^1)=S^1 \times S^1$. (Unsure how to express this, but hopefully this is clear enough.)   Then $A\cap B=S^1\times \{\text{point}\}=S^1$ and $A\cup B=X$.  The Mayer-Vietoris sequence then gives us an exact sequence in reduced homology as follows:  $$0 \to \mathbb{Z}^2 \to \tilde{H}_2(X) \to \mathbb{Z} \to \mathbb{Z}^2 \to \tilde{H}_1(X) \to 0.$$  Is it possible from this exact sequence to determine the homology groups, in some algebraic fashion? Or do I need to determine what the maps are? How do I determine the maps? In C#, what is the best way to access a property of the derived class when the generic list contains just the base class.  public class ClassA : BaseClass {    public object PropertyA { get; set; } }  public class ClassB: BaseClass {     public object PropertyB { get; set; } }  public class BaseClass { }  public void Main {     List&lt;BaseClass&gt; MyList = new List&lt;BaseClass&gt;();     ClassA a = new ClassA();     ClassB b = new ClassB();      MyList.Add(a);     MyList.Add(b);      for(int i = 0; i &lt; MyList.Count; i++)     {         //I would like to access PropertyA abd PropertyB from the derived classes             } } For f continuous on $[0,1]$, show that there exist points $\alpha_k$ such that $\sum \limits_{k=1}^n \frac{1}{f'(\alpha_k)} = n $ Suppose that $f$ is continous on $[0,1]$ , differentiable on $(0,1)$ , and $f(0)=0$ and  $f(1)=1$.For every integer $n$ show  that there must exist $n$ distinct points $\alpha_1,\alpha_2\cdots,\alpha_n$ in that interval so that    $\sum \limits_{k=1}^n \frac{1}{f'(\alpha_k)} = n $   Is it theorem or i can show it with basic differentiation knowledge .Please give me hint . As the title says: Is a 1st-level spell cast using a 4th-level slot a 1st-level spell, or a 4th-level spell? How to check if jQuery.ajax() request header Status is "304 Not Modified"? Antisymmetric Relations This is a "catch-all" question designed to serve as an answer for all questions about choosing web hosting.  Pro Webmasters no longer accepts new questions about how to choose hosting.  All future questions pertaining to finding web hosting should be closed as a duplicate of this question. For more information about this policy please see .    How to find web hosting that meets my requirements?  What we're looking for in answers to this question are the basics about web hosting:   What is web hosting? What is the difference between shared, VPS, and dedicated hosting? How does a content delivery network relate to web hosting? Anything else you feel is helpful in finding a web host.   What we do not want is:   Endorsements or recommendations for specific web hosts We do not want your experience or other subjective information (just the facts please) Story where vampires are created by drop absorbed on neck? I have been trying to identify a book that I read maybe 25-30 years ago (1987-1992), in which there are vampire or vampire-like creatures, but instead of being created in the traditional way (e.g. bite on the neck), something drops a drop of a fluid on the back of their neck, which is then absorbed into the body and transforms them. I have a vague notion that some sort of tree is what creates these drops. The drops may have had a shiny metallic appearance.  I've tried to find this book before and always came up short. I'm starting to think the whole thing was a dream and I never read it at all. But I really feel like it was a book or at least a short story. In C#, I want to initialize a string value with an empty string.  How should I do this?  What is the right way, and why?  string willi = string.Empty;   or  string willi = String.Empty;   or  string willi = "";   or what? How can I explain to people that the phrase “off of ” is grammatically incorrect? NSArray becomes NSCFArray when passed I have a dual boot of Windows 10 and Ubuntu 16.04. Recently I upgraded it to 18.04. As soon as I did it, it started showing DISK IS LIKELY TO FAIL SOON (37° C / 99° F).    I checked the status of my disk via Windows and it shows it’s perfectly healthy. I assumed the error occurred because my partition size of Ubuntu was 64GB (which I now increased to 86GB). Please help me out with this.    Edit: The results of smartctl - attributes How to avoid perceived circularity when defining a formal language? Suppose we want to define a first-order language to do set theory (so we can formalize mathematics). One such construction can be found . What makes me uneasy about this definition is that words such as "set", "countable", "function", and "number" are used in somewhat non-trivial manners. For instance, behind the word "countable" rests an immense amount of mathematical knowledge: one needs the notion of a bijection, which requires functions and sets. One also needs the set of natural numbers (or something with equal cardinality), in order to say that countable sets have a bijection with the set of natural numbers.  Also, in set theory one uses the relation of belonging "$\in$". But relation seems to require the notion an ordered pair, which requires sets, whose properties are described using belonging...  I found the following in Kevin Klement's,  (pages 2-3).  "You have to use logic to study logic. There’s no getting away from it. However, I’m not going to bother stating all the logical rules that are valid in the metalanguage, since I’d need to do that in the metametalanguage, and that would just get me started on an infinite regress. The rule of thumb is: if it’s OK in the object language, it’s OK in the metalanguage too."  So it seems that, if one proves a fact about the object language, then one can also use it in the metalanguage. In the case of set theory, one may not start out knowing what sets really are, but after one proves some fact about them (e.g., that there are uncountable sets) then one implicitly "adds" this fact also to the metalanguage.  This seems like cheating: one is using the object language to conduct proofs regarding the metalanguage, when it should strictly be the other way round.  To give an example of avoiding circularity, consider the definition of the integers. We can define a binary relation $R\subseteq(\mathbf{N}\times\mathbf{N})\times(\mathbf{N}\times\mathbf{N})$, where for any $a,b,c,d\in\mathbf{N}$, $((a,b),(c,d))\in R$ iff $a+d=b+c$, and then defining $\mathbf{Z}:= \{[(a,b)]:a,b\in\mathbf{N}\}$, where $[a,b]=\{x\in \mathbf{N}\times\mathbf{N}: xR(a,b)\}$, as in  question or  on Wikipedia. In this definition if set theory and natural numbers are assumed, then there is no circularity because one did not depend on the notion of "subtraction" in defining the integers.  So my question is:     Question Is the definition of first-order logic circular?   If not, please explain why.   If the definitions are circular, is there an alternative definition which avoids the circularity?   Some thoughts:   Perhaps there is the distinction between what sets are (anything that obeys the axioms) and how sets are expressed (using a formal language). In other words, the notion of a set may not be circular, but to talk of sets using a formal language requires the notion of a set in a metalanguage. In foundational mathematics there also seems to be the idea of first defining something, and then coming back with better machinery to analyse that thing. For instance, one can define the natural numbers using the Peano axioms, then later come back to say that all structures satisfying the axioms are isomorphic. (I don't know any algebra, but that seems right.) Maybe sets, functions, etc., are too basic? Is it possible to avoid these terms when defining a formal language? How to make a water vortex I'm very new to Blender and I'm trying to make a water vortex like this.(may be not the easyest first project for a newbie)     I watched several tutorial on liquids particle etc but I'm not sure what is the best aproach. What I tried  until now:   I made a particle system with a vortex force field. It looks good, but I'm not able to add the right material.      I played around with the fluid physics, the water looks good but if I add a vortex force field it does nothing.   I would be very grateful if somebody could point me in the right direction because I'm definitely stocked. Today I came across an ad on this question on SO:  (I don't expect it to stay very long).   There was a community promotion ad on the right hand side of the site, I think for one of our English sites. It had a sentence that I only partially remember:     Idiom ... poor or even poorer   I found it interesting, so I clicked that ad. Which caused a new instance of SO to open within the ad space. Unfortunately I failed to take a screenshot. I've been refreshing the page like crazy, but can't get the ad to appear again.  Edit: I managed to get a new community add, for the photography site, and captured a screenshot:   Edit2: This bug still persists, I saw it today with an OOP add from CodeReview, and an area 51 add. Using (or not) the word "to" in a sentence ending with "be able" Unable to get force:inputField or force:outputField to render inside other markup in Lightning Component when used in Lightning Experience How does one add boarding passes to Apple Wallet?