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  • NoneType has no attribute Append

    - by Rosarch
    I'm new to Python. I can't understand why a variable is None at a certain point in my code: class UsersInRoom(webapp.RequestHandler): def get(self): room_id = self.request.get("room_id") username = self.request.get("username") UserInRoom_entities = UserInRoom.gql("WHERE room = :1", room_id).get() if UserInRoom_entities: for user_in_room in UserInRoom_entities: if user_in_room.username == username: user_in_room.put() # last_poll auto updates to now whenenever user_in_room is saved else: user_in_room = UserInRoom() user_in_room.username = username user_in_room.put() UserInRoom_entities = [] UserInRoom_entities.append(user_in_room) // error here # name is `user_at_room` intead of `user_in_room` to avoid confusion usernames = [user_at_room.username for user_at_room in UserInRoom_entities] self.response.out.write(json.dumps(usernames)) The error is: Traceback (most recent call last): File "C:\Program Files\Google\google_appengine\google\appengine\ext\webapp\__init__.py", line 507, in __call__ handler.get(*groups) File "path\to\chat.py", line 160, in get AttributeError: 'NoneType' object has no attribute 'append' How is this possible? I'm setting UserInRoom_entities = [] immediately before that call. Or is something else the None in question?

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  • Python: combine two neighbor list components

    - by kame
    When i use this code I get elements wich containing one number or letter. How to combine two neighbors? data = '4D41544C414220352E30204D41542D66696C652C20506C6174666F726D3A20504357494E2C2043726561746564206F6E3A20576564204D61792030352031363A31393A3337203230313020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020202020200001494D0F00000026000000789CE36360607000623620E680D220C00AE53343312310BA00692620E604F351010025BE00C8' data2 = list(data) print data2

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  • How to make simple mathematical operations and displaying the result in a textbox

    - by Audel
    Hi, I know is a rather simple question but I just can't find an appropriate example in google or anywhere. I've got this piece int numberOfPlays = int.Parse(textBox2.Text); numberOfPlays = (numberOfPlays++); textBox2.Text = (numberOfPlays.ToString()); MessageBox.Show(numberOfPlays.ToString()); So basically what I want to do is to get the value of the textBox2, make it an integer and then add 1 to it. I can't think of any more details right now, so if i'm not clear enough please ask Thanks in advance

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  • SQL-wrappers (activerecord) to recommened for python?

    - by Horace Ho
    is there an activerecord (any similar SQL-wrapper) for python? which is good for: used in a server-side python script light-weight supports MySQL what I need to do: insert (filename, file size, file md5, the file itself) into (string, int, string, BLOB) columns if the same file (checksum + filename) does not exist in db thx

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  • Is there an algorithm for finding an item that matches certain properties, like a 20 questions game?

    - by lala
    A question about 20 questions games was asked here: However, if I'm understanding it correctly, the answers seem to assume that each question will go down a hierarchal branching tree. A binary tree should work if the game went like this: Is it an animal? Yes. Is it a mammal? Yes. Is it a feline? Yes. Because feline is an example of a mammal and mammal is an example of an animal. But what if the questions go like this? Is it a mammal? Yes. Is it a predator? Yes. Does it have a long nose? No. You can't branch down a tree with those kinds of questions, because there are plenty of predators that aren't mammals. So you can't have your program just narrow it down to mammal and have predators be a subset of mammals. So is there a way to use a binary search tree that I'm not understanding or is there a different algorithm for this problem?

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  • Passing object through WCF so that server receives client changes

    - by cvig
    I would like to set up a WCF service so that any changes a client makes to an object I send them are also reflected on the server side. For example, if Assembly A has the following... namespace AssemblyA { public class Person { public string FirstName { get; set; } public string LastName { get; set; } } [ServiceContract] public interface IServer { [OperationContract] Person GetPerson(); } } And Assembly B references Assembly A... using AssemblyA; namespace AssemblyB { class Program { static void Main(string[] args) { <snip> IServer server = factory.CreateChannel(); Person person = server.GetPerson(); person.FirstName = "Kilroy"; person.LastName = "WuzHere"; } } } What is the easiest/best way to make it so that the service's copy of the Person object also reflects the changes that the client makes? Is this even possible?

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  • printing the instance in Python

    - by kame
    Hello! With this code: class Complex: def __init__(self, realpart, imagpart): self.real = realpart self.imag = imagpart print self.real, self.imag class Circle: def __init__(self, radius): print "A circle wiht the radius", radius, "has the properties:" print "circumference =", 3.14*radius print "area =", 3.14*radius**2 I get this output: >>> Complex(3,2) 3 2 <__main__.Complex instance at 0x01412210> But why does he print the last line?

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  • Java: global values inside a class?

    - by HH
    I want less methods. I want a common global TestClass from which I could use any of its value inside the class. import java.util.*; import java.io.*; public class TestClass { TestClass(String hello){ String hallo = hello; String halloSecond = "Saluto!"; } public static void main(String[] args) { TestClass test = new TestClass("Tjena!"); System.out.println("I want "Tjena!": " + test.hallo); TestClass testSecond = new TestClass("1"); System.out.println("I want Saluto!:" + test.halloSecond); System.out.println("I want Saluto!:" + testSecond.halloSecond); } }

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  • Where can I find Python tutorials aimed at people who are already programmers?

    - by Chris R
    I'm a reasonably skilled programmer, and I'm interested in branching out into some new languages -- python, specifically -- but frankly I do NOT want to go through a tutorial that assumes I know nothing about programming. I want a tutorial -- again, preferably for python -- that assumes I'm just unfamiliar with the language itself and describes the ways I can use the language to solve problems. Does such a beast exist? I mean, other than the Python wiki?

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  • Am I doing something wrong here (references in C++)?

    - by m4design
    I've been playing around with references (I'm still having issues in this regard). 1- I would like to know if this is an acceptable code: int & foo(int &y) { return y; // is this wrong? } int main() { int x = 0; cout << foo(x) << endl; foo(x) = 9; // is this wrong? cout << x << endl; return 0; } 2- Also this is from an exam sample: Week & Week::highestSalesWeek(Week aYear[52]) { Week max = aYear[0]; for(int i = 1; i < 52; i++) { if (aYear[i].getSales() > max.getSales()) max = aYear[i]; } return max; } It asks about the mistake in this code, also how to fix it. My guess is that it return a local reference. The fix is: Week & max = aYear[0]; Is this correct/enough?

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  • Writing a file shredder in python or ruby?

    - by pmilb21
    In the effort to learn python and/or ruby, I was wondering how a file shredder would be implemented? I would like it to take in a file as an argument and then employ an algorithm to make that file unrecoverable. Would possibly add the support for multiple files or even whole directories later.

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  • Codeigniter: URI segments

    - by Kevin Brown
    How do I create an if statement saying something like this? $segment = "segment 2 or 3"; if($segment == 1{ do stuff } I know this is pretty elementary, but I don't totally understand the URI class...

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  • How to set a predefined value in a form in Rails

    - by marco
    So I just got started in Rails, and I'm trying to create an Object (a book_loan in my case) with a Form. The thing is that I get to this form by clicking on a book, so I pass the book_id as a parameter, like localhost:3000/loans/new?id=1. Now I don't want the user to be able to set the book id field in the form, since I already know the id. So my question is how to set the value in the form. I have been trying things like: <% form_for(@loan) do |f| %> <%= f.error_messages %> ... <%= @loan.book_id = params[:id] %> <%= f.submit 'Create' %> <% end %> without any success. Does anybody have a hint for me?

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  • How to pass objects to functions in C++?

    - by Rakesh K
    I am new to C++ programming, but I have experience in Java. I need guidance on how to pass objects to functions in C++. Do I need to pass pointers, references, or non-pointer and non-reference values? I remember in Java there are no such issues since we pass just the variable that holds reference to the objects. It would be great if you could also explain where to use each of those options.

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  • Replacing emty csv column values with a zero

    - by homerjay
    Hey, So I'm dealing with a csv file that has missing values. What I want my script to is: #!/usr/bin/python import csv import sys #1. Place each record of a file in a list. #2. Iterate thru each element of the list and get its length. #3. If the length is less than one replace with value x. reader = csv.reader(open(sys.argv[1], "rb")) for row in reader: for x in row[:]: if len(x)< 1: x = 0 print x print row Here is an example of data, I trying it on, ideally it should work on any column lenghth Before: actnum,col2,col4 xxxxx , , xxxxx , 845 , xxxxx , ,545 After actnum,col2,col4 xxxxx , 0 , 0 xxxxx , 845, 0 xxxxx , 0 ,545 Any guidance would be appreciated

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  • How to test if an array contains a pair of numbers whose product is odd?

    - by John
    How can I write a function that takes an array of integers and returns true if their exists a pair of numbers whose product is odd? What are the properties of odd integers? And of course, how do you write this function in Java? Also, maybe a short explanation of how you went about formulating an algorithm for the actual implementation. Yes, this is a function out of a textbook. No, this is not homework—I'm just trying to learn, so please no "do your own homework comments."

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