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  • What is the proper response to lousy error message?

    - by William Pursell
    I've just come across (for the 47 millionth time) some code that looks like this: except IOError, e: print "Problems reading file: %s." % filename sys.exit( 1 ) My first reaction is very visceral: the person who coded this is a complete idiot. How hard is it to print error messages to stderr and to include the system error message in the string? I haven't used python in years, and it took me all of 4 minutes to track down the documentation to figure out how to get the error message from the exception object e and the syntax for printing to stderr. My "complete idiot" reaction was slightly lessened since at least a non-zero value is passed to sys.exit, but I still find this code offensive. My prime thought is that the developer who wrote this is a complete novice for whom I have zero respect. Am I over-reacting? Surely there are excuses for all sorts of bad coding practices, but is there anything that can possibly excuse this sort of $#|t? I guess there are two question here: one is a duplicate of What are developer's problems with helpful error messages?, and the other is "am I over-reacting, or is it valid to conclude that the author of the above code is a novice?"

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  • Caching factory design

    - by max
    I have a factory class XFactory that creates objects of class X. Instances of X are very large, so the main purpose of the factory is to cache them, as transparently to the client code as possible. Objects of class X are immutable, so the following code seems reasonable: # module xfactory.py import x class XFactory: _registry = {} def get_x(self, arg1, arg2, use_cache = True): if use_cache: hash_id = hash((arg1, arg2)) if hash_id in _registry: return _registry[hash_id] obj = x.X(arg1, arg2) _registry[hash_id] = obj return obj # module x.py class X: # ... Is it a good pattern? (I know it's not the actual Factory Pattern.) Is there anything I should change? Now, I find that sometimes I want to cache X objects to disk. I'll use pickle for that purpose, and store as values in the _registry the filenames of the pickled objects instead of references to the objects. Of course, _registry itself would have to be stored persistently (perhaps in a pickle file of its own, in a text file, in a database, or simply by giving pickle files the filenames that contain hash_id). Except now the validity of the cached object depends not only on the parameters passed to get_x(), but also on the version of the code that created these objects. Strictly speaking, even a memory-cached object could become invalid if someone modifies x.py or any of its dependencies, and reloads it while the program is running. So far I ignored this danger since it seems unlikely for my application. But I certainly cannot ignore it when my objects are cached to persistent storage. What can I do? I suppose I could make the hash_id more robust by calculating hash of a tuple that contains arguments arg1 and arg2, as well as the filename and last modified date for x.py and every module and data file that it (recursively) depends on. To help delete cache files that won't ever be useful again, I'd add to the _registry the unhashed representation of the modified dates for each record. But even this solution isn't 100% safe since theoretically someone might load a module dynamically, and I wouldn't know about it from statically analyzing the source code. If I go all out and assume every file in the project is a dependency, the mechanism will still break if some module grabs data from an external website, etc.). In addition, the frequency of changes in x.py and its dependencies is quite high, leading to heavy cache invalidation. Thus, I figured I might as well give up some safety, and only invalidate the cache only when there is an obvious mismatch. This means that class X would have a class-level cache validation identifier that should be changed whenever the developer believes a change happened that should invalidate the cache. (With multiple developers, a separate invalidation identifier is required for each.) This identifier is hashed along with arg1 and arg2 and becomes part of the hash keys stored in _registry. Since developers may forget to update the validation identifier or not realize that they invalidated existing cache, it would seem better to add another validation mechanism: class X can have a method that returns all the known "traits" of X. For instance, if X is a table, I might add the names of all the columns. The hash calculation will include the traits as well. I can write this code, but I am afraid that I'm missing something important; and I'm also wondering if perhaps there's a framework or package that can do all of this stuff already. Ideally, I'd like to combine in-memory and disk-based caching.

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  • How bad is it to have two methods with the same name but different signatures in two classes?

    - by Super User
    I have a design problem related to a public interface, the names of methods, and the understanding of my API and code. I have two classes like this: class A: ... function collision(self): .... ... class B: .... function _collision(self, another_object, l, r, t, b): .... The first class has one public method named collision, and the second has one private method called _collision. The two methods differs in argument type and number. As an example let's say that _collision checks if the object is colliding with another object with certain conditions l, r, t, b (collide on the left side, right side, etc) and returns true or false. The public collision method, on the other hand, resolves all the collisions of the object with other objects. The two methods have the same name because I think it's better to avoid overloading the design with different names for methods that do almost the same thing, but in distinct contexts and classes. Is this clear enough to the reader or I should change the method's name?

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  • Parallel.For Inconsistency results

    - by ni Gue ???
    I am using VB.net to write a parallel based code. I use Parallel.For to generate pairs of 500 objects or in combination C(500,2) such as the following code; but I found that it didn't always generate all combinations which should be 124750 (shown from variable Counter). No other thread was runing when this code was run. I am using a Win-7 32 Bit desktop with Intel Core i5 CPU [email protected], 3.33 GHz and RAM 2GB. What's wrong with the code and how to solve this problem? Thank You. Dim Counter As Integer = 0 Parallel.For(0, 499, Sub(i) For j As Integer = i + 1 To 499 Counter += 1 Console.Write(i & ":" & j) Next End Sub) Console.Writeline("Iteration number: " & Counter)

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  • How can a collection class instantiate many objects with one database call?

    - by Buttle Butkus
    I have a baseClass where I do not want public setters. I have a load($id) method that will retrieve the data for that object from the db. I have been using static class methods like getBy($property,$values) to return multiple class objects using a single database call. But some people say that static methods are not OOP. So now I'm trying to create a baseClassCollection that can do the same thing. But it can't, because it cannot access protected setters. I don't want everyone to be able to set the object's data. But it seems that it is an all-or-nothing proposition. I cannot give just the collection class access to the setters. I've seen a solution using debug_backtrace() but that seems inelegant. I'm moving toward just making the setters public. Are there any other solutions? Or should I even be looking for other solutions?

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  • How to approach iOS web clip app "download"?

    - by Ryan
    We have our main site at: http://mysite.com which we don't want to alter. Then we have our web clip app at: http://mysite.com/app/ If someone visits the app URL in normal Safari then the Safari UI will still display. But if the user adds the app URL to their home screen, and then they tap that icon they will launch the app URL without the Safari UI as intended. My question is how do you go about getting the user to use the web clip app from their home screen when they start from mysite.com? What I'm thinking is that we have a link on mysite.com that points to mysite.com/app/. Then when they click that /app/ link they'll go to the app but it won't be in "app mode". Can I detect that it's not in app mode and display a message like "add this page to your home screen to use the app"? And then when they do visit in app mode obviously just let the app run.

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  • Your experiences with TDD [closed]

    - by SkonJeet
    In your experience, does TDD prove to be a useful approach in all development projects? Do you take the approach of TDD even when working on an existing project? Also, how does mocking tie in with a TDD discipline? I'm not looking for opinions, I'm looking for developers' advice, tips and learning resources regarding TDD's usage based on their experience. I'm going to spend the day equipping myself with enough knowledge about TDD to start making small steps towards using it but I don't know to what extent I should be using it.

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  • Need advice on framework design: how to make extending easy

    - by beginner_
    I'm creating a framework/library for a rather specific use-case (data type). It uses diverse spring components, including spring-data. The library has a set of entity classes properly set up and according service and dao layers. The main work or main benefit of the framework lies in the dao and service layer. Developers using the framework should be able to extend my entity classes to add additional fields they require. Therefore I made dao and service layer generic so it can be used by such extended entity classes. I now face an issue in the IO part of the framework. It must be able to import the according "special data type" into the database. In this part I need to create a new entity instance and hence need the actual class used. My current solution is to configure in spring a bean of the actual class used. The problem with this is that an application using the framework could only use 1 implementation of the entity (the original one from me or exactly 1 subclass but not 2 different classes of the same hierarchy. I'm looking for suggestions / desgins for solving this issue. Any ideas?

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  • Are first-class functions a substitute for the Strategy pattern?

    - by Prog
    The Strategy design pattern is often regarded as a substitute for first-class functions in languages that lack them. So for example say you wanted to pass functionality into an object. In Java you'd have to pass in the object another object which encapsulates the desired behavior. In a language such as Ruby, you'd just pass the functionality itself in the form of an annonymous function. However I was thinking about it and decided that maybe Strategy offers more than a plain annonymous function does. This is because an object can hold state that exists independently of the period when it's method runs. However an annonymous function by itself can only hold state that ceases to exist the moment the function finishes execution. So my question is: when using a language that features first-class functions, would you ever use the Strategy pattern (i.e. encapsulate the functionality you want to pass around in an explicit object), or would you always use an annonymous function? When would you decide to use Strategy when you can use a first-class function?

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  • is it possible to change from software developer job to business analyst job

    - by user72406
    I am working as a software developer (.net programmer) for an mnc for the past two years. From the initial days itself I know I am not a good programer at all, but I tried learning and managed the development for these two years. I am looking to do mba in future and move to business side. But to start mba I need an year more. I don't want to continue programing in this year. I am looking for a change in position which will help me doing my mba too. Please suggest.

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  • errors with libosmscout [migrated]

    - by Katlego Moukangwe
    I am using the libosmscout library for routing and I get the following error when I run the Routing demo; Routing . 169639811 169639816 169639831 253045594 //Running the routing demo with the map in the current directory. Cannot get start way! There was an error while calculating the route! I think It might be during the import stage since I get the following warnings; !! Cannot resolve way member 28693141 for relation 28322 boundary_administrative Mecklenburg-Vorpommern !! Cannot resolve way member 152675051 for relation 28936 boundary_administrative Bergedorf !! Cannot resolve way member 26496646 for relation 28964 boundary_administrative Harburg (Hamburg) !! Node 323985058 of way 135078286 cannot be joined with any other way of the relation 1817154 Neuenkirchen WW Multipolygon relation 2136137 has conflicting types for outer boundary (place_island vs. boundary_administrative) !! Cannot resolve way member 162656856 for relation 2174826 landuse_forest

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  • If you had two projects with the same specification and only one was developed using TDD how could you tell?

    - by Andrew
    I was asked this question in an interview and it has been bugging me ever since. You have two projects, both with the same specification but only one of these projects was developed using Test Driven Development. You are given the source for both but with the tests removed from the TDD project. How can you tell which was developed using TDD? All I was able to muster up was something about the classes being more 'broken up' in to smaller chunks and having more visible APIs, not my proudest moment. I would be very interested to hear a good answer to this question.

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  • Interview questions for programming tutor?

    - by Emmett Gear
    My family is looking for a programming/computer science tutor. Personally, I want to learn Java or some other brand of web programming. I am best described as a PC "power user." I have never programmed in the past and would like a good jump start. I am a very quick learner and do not expect the tutor to have to teach me the ultra basic stuff that I can learn myself. My son also needs a programming tutor. He just got into Carnegie Mellon as a computer science major. Having done only robotics and mathematics in the past he is very nervous that he does not have the same level of knowledge as his future classmates. I need some help coming up with a list of questions to ask potential tutors and some criteria to judge them by. Thanks! Edit: So far I have come up with just the obvious... Where did you receive your education? What languages are you familiar with? How long have you been tutoring? What made you decide to become a tutor? What software projects have you worked on? What work references can you give me? How much do you charge?

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  • What are the so-called "levels" of understanding multithreading?

    - by Dan Tao
    I seem to remember reading somewhere some list of 4 "levels" of understanding multithreading. This may have been in a formal publication, or it may have been in an extremely informal context (even like in a Stack Overflow question, for example). Unfortunately I don't remember who referred to them or precisely what they were. I seem to recall that they were roughly like: Total ignorance Awareness mixed with incompetence Relative competence mixed with fear True understanding My intention is to refer to these levels in a blog post I'm writing, with a reference; but I can't for the life of me remember where I first encountered this list. Brief Google searches have proved unfruitful.

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  • Breaking up a large PHP object used to abstract the database. Best practices?

    - by John Kershaw
    Two years ago it was thought a single object with functions such as $database->get_user_from_id($ID) would be a good idea. The functions return objects (not arrays), and the front-end code never worries about the database. This was great, until we started growing the database. There's now 30+ tables, and around 150 functions in the database object. It's getting impractical and unmanageable and I'm going to be breaking it up. What is a good solution to this problem? The project is large, so there's a limit to the extent I can change things. My current plan is to extend the current object for each table, then have the database object contain these. So, the above example would turn into (assume "user" is a table) $database->user->get_user_from_id($ID). Instead of one large file, we would have a file for every table.

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  • Is encoding needed in this decryption?

    - by Lijo
    I have a Encryption – Decryption scenario as shown below. //[Clear text ID string as input] -- [(ASCII GetByte) + Encoding] -- [Encrption as byte array] -- [Database column is in VarBinary] -- [Pass byte[] as VarBinary parameter to SP for comparison] //[ID stored as VarBinary in Database] -- [Read as byte array] -- [(Decrypt as byte array) + Encoding + (ASCII Get String)] -- Show as string in the UI My question is in the decryption scenario. After decryption I get a byte array. I am doing an encoding (IBM037) after that. Is it correct? Is there something wrong in the flow shown above? private static byte[] GetEncryptedID(string id) { Interface_Request input = new Interface_Request(); input.RequestText = Encodeto64(id); input.RequestType = Encryption; ProgramInterface inputRequest = new ProgramInterface(); inputRequest.Test_Trial_Request = input; using (KTestService operation = new KTestService()) { return ((operation.KTrialOperation(inputRequest)).Test_Trial_Response.ResponseText); } } private static string GetDecryptedID(byte[] id) { Interface_Request input = new Interface_Request(); input.RequestText = id; input.RequestType = Decryption; ProgramInterface request = new ProgramInterface(); request.Test_Trial_Request = input; using (KTestService operationD = new KTestService()) { ProgramInterface1 response = operationD.KI014Operation(request); byte[] decryptedValue = response.ICSF_AES_Response.ResponseText; Encoding sourceByteFormat = Encoding.GetEncoding("IBM037"); Encoding destinationByteFormat = Encoding.ASCII; //Convert from one byte format to other (IBM to ASCII) byte[] ibmEncodedBytes = Encoding.Convert(sourceByteFormat, destinationByteFormat,decryptedValue); return System.Text.ASCIIEncoding.ASCII.GetString(ibmEncodedBytes); } } private static byte[] EncodeTo64(string toEncode) { byte[] dataInBytes = System.Text.ASCIIEncoding.ASCII.GetBytes(toEncode); Encoding destinationByteFormat = Encoding.GetEncoding("IBM037"); Encoding sourceByteFormat = Encoding.ASCII; //Convert from one byte format to other (ASCII to IBM) byte[] asciiBytes = Encoding.Convert(sourceByteFormat, destinationByteFormat, dataInBytes); return asciiBytes; }

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  • which style of member-access is preferable

    - by itwasntpete
    the purpose of oop using classes is to encapsulate members from the outer space. i always read that accessing members should be done by methods. for example: template<typename T> class foo_1 { T state_; public: // following below }; the most common doing that by my professor was to have a get and set method. // variant 1 T const& getState() { return state_; } void setState(T const& v) { state_ = v; } or like this: // variant 2 // in my opinion it is easier to read T const& state() { return state_; } void state(T const& v) { state_ = v; } assume the state_ is a variable, which is checked periodically and there is no need to ensure the value (state) is consistent. Is there any disadvantage of accessing the state by reference? for example: // variant 3 // do it by reference T& state() { return state_; } or even directly, if I declare the variable as public. template<typename T> class foo { public: // variant 4 T state; }; In variant 4 I could even ensure consistence by using c++11 atomic. So my question is, which one should I prefer?, Is there any coding standard which would decline one of these pattern? for some code see here

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  • Why does java.util.ArrayList allow to add null?

    - by Alfredo O
    I wonder why java.util.ArrayList allows to add null. Is there any case where I would want to add null to an ArrayList? I am asking this question because in a project we had a bug where some code was adding nulls to the List and it was hard to spot where the bug was. Obviously a NullPointerException was thrown but not until another code tried to access the element. The problem was how to locate the code that added the null object. It would have been easier if the ArrayList throwed an exception in the code where the elements was being added.

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  • Situations that require protecting files against tampering when stored on a users computer

    - by Joel
    I'm making a 'Pokémon Storage System' with a Client/Server model and as part of that I was thinking of storing an inventory file on the users computer which I do not wish to be edited except by my program. An alternative to this would be to instead to store the inventory file on the server and control it's editing by sending commands to the server but I was wondering if there are any situations which require files to be stored on a users computer where editing would be undesirable and if so how do you protect the files? I was thinking AES with some sort of checksum?

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  • Please, tell us how you made Agile work for you?

    - by Paul
    I've been seeing many questions related to Agile. There seems to be confusion between the people who are doing Agile successfully, and those of us who don't understand it. So I'm wondering if some of the successful teams would be willing to give the result of us some examples of how you succeeded. Some of the things I know I wonder What steps did you use? (ie. Talk to users, mock up, tests, code, testing, (whatever)) Tools that helped you? Did you generate any artifacts, other than a working implementation? How did you prevent spaghetti architecture / code? How do you pass along to new team members, or is the team stable for the project How did you determine exit criteria, or was it open ended. (Scope of project?) Did you do this as contracting? How did you develop a contract up-front? Did the business do any up front work? Or did they come to the table with "We want to implement a "bleh bleh blah"? What types of tests did you use? Unit, Integration, UAT? Or did the process make some/all of those unnecessary? Bonus: Do you have an situations / links to "How To" Agile articles, books, etc? Wiki, describes what but not how (to the uninitiated) At least to me, not a duplicate

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  • Algorithmic problem - quickly finding all #'s where value %x is some given value

    - by Steve B.
    Problem I'm trying to solve, apologies in advance for the length: Given a large number of stored records, each with a unique (String) field S. I'd like to be able to find through an indexed query all records where Hash(S) % N == K for any arbitrary N, K (e.g. given a million strings, find all strings where HashCode(s) % 17 = 5. Is there some way of memoizing this so that we can quickly answer any question of this form without doing the % on every value? The motivation for this is a system of N distributed nodes, where each record has to be assigned to at least one node. The nodes are numbered 0 - (K-1) , and each node has to load up all of the records that match it's number: If we have 3 nodes Node 0 loads all records where Hash % 3 ==0 Node 1 loads all records where Hash % 3 ==1 Node 2 loads all records where Hash % 3 ==2 adding a 4th node, obviously all the assignments have to be recomputed - Node 0 loads all records where Hash % 4 ==0 ... etc I'd like to easily find these records through an indexed query without having to compute the mod individually. The best I've been able to come up with so far: If we take the prime factors of N (p1 * p2 * ... ) if N % M == I then p % M == I % p for all of N's prime factors e.g. 10 nodes : N % 10 == 6 then N % 2 = 0 == 6 %2 N % 5 = 1 == 6 %5 so storing an array of the "%" of N for the first "reasonable" number of primes for my data set should be helpful. For example in the above example we store the hash and the primes HASH PRIMES (array of %2, %3, %5, %7, ... ]) 16 [0 1 1 2 .. ] so looking for N%10 == 6 is equivalent to looking for all values where array[1]==1 and array[2] == 1. However, this breaks at the first prime larger than the highest number I'm storing in the factor table. Is there a better way?

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  • How many developers do I need to build a website like Freelancer.com in about 3-5 months? [closed]

    - by Sam
    I have been asked to make a list of people that I need to build something similar to freelancer.com. Not exactly same, has a few more features to it too but I can't really get my head around the whole freelancer.com site. I have built a social networking site from scratch which is 70% of Facebook and 20% Google+ in about 5 months with raw PHP, JS, CSS and Ajax. I dont think it will take me more than a month or something to build the whole freelancer.com from scratch. Please suggest anything that should I pay attention to. I am thinking about: 2 php developers 1 mysql engineer 1 network/server engineer 1 graphics artist 1 UI developer Time frame: 20 days Is this a good estimation?

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  • Do you leverage the benefits of the open-closed principle?

    - by Kaleb Pederson
    The open-closed principle (OCP) states that an object should be open for extension but closed for modification. I believe I understand it and use it in conjunction with SRP to create classes that do only one thing. And, I try to create many small methods that make it possible to extract out all the behavior controls into methods that may be extended or overridden in some subclass. Thus, I end up with classes that have many extension points, be it through: dependency injection and composition, events, delegation, etc. Consider the following a simple, extendable class: class PaycheckCalculator { // ... protected decimal GetOvertimeFactor() { return 2.0M; } } Now say, for example, that the OvertimeFactor changes to 1.5. Since the above class was designed to be extended, I can easily subclass and return a different OvertimeFactor. But... despite the class being designed for extension and adhering to OCP, I'll modify the single method in question, rather than subclassing and overridding the method in question and then re-wiring my objects in my IoC container. As a result I've violated part of what OCP attempts to accomplish. It feels like I'm just being lazy because the above is a bit easier. Am I misunderstanding OCP? Should I really be doing something different? Do you leverage the benefits of OCP differently? Update: based on the answers it looks like this contrived example is a poor one for a number of different reasons. The main intent of the example was to demonstrate that the class was designed to be extended by providing methods that when overridden would alter the behavior of public methods without the need for changing internal or private code. Still, I definitely misunderstood OCP.

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  • How can I turn off calculated columns in an Excel table from a macro using VBA? [migrated]

    - by user41293
    I am working on a macro that inserts formulas into a cell in an Excel table. The Excel table does the automatic filling of columns and fills all the cells in that column with the formula, but all I want is one cell to have the formula. I cannot just turn off automatic formula for tables as I need to have other people use this worksheet on their systems. Is there a way to turn off the automatic filling of formulas in a table using VBA in a macro? It just needs to be temporary: I just want to turn it off, put in my formulas, then turn it back on.

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  • As a developer, how do I learn sales? [closed]

    - by Dan Abramov
    I quit the company I was working for to pursuit an opportunity as a startup, and I believe in our product. I'm sure it's going to be great if we attract some customers first to keep going. (I don't want funding.) Our product is targeted at private schools and courses, and helps organize the mess other LMSs introduce. The problem is, our team is basically just me and I have very little idea about sales and marketing. I can do reasonably good copywriting but I'm sure I can do better—and being nervous or too techy in a real world conversation with the client doesn't help. I want to get better, in fact, a lot better at negotiating with clients and pitching my product. I did look for some “sales articles” on the web, and a lot of what I found is plain bullshit on SEO-engineered websites promoting books or $5000 courses. What I need instead is a developer's perspective on how to sale a product you think is great. What are typical programmer's mistakes and misconceptions about sales, and how to avoid them? How do you evolve into a reasonably great salesman? I can't believe it's in the mindset and unlearnable. Your own experience, combined with great articles available on the web is most welcome. To Future Readers The question got closed because it is not a good fit for this site. I found some helpful tips in a similar question asked on a sister StackExchange site about startups: I'm a terrible salesperson. What can I do about it?

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