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• Python: why does str() on some text from a UTF-8 file give a UnicodeDecodeError?

  - by AP257

  I'm processing a UTF-8 file in Python, and have used simplejson to load it into a dictionary. However, I'm getting a UnicodeDecodeError when I try to turn one of the dictionary values into a string: f = open('my_json.json', 'r') master_dictionary = json.load(f) #some json wrangling, then it fails on this line... mysql_string += " ('" + str(v_dict['code']) Traceback (most recent call last): File "my_file.py", line 25, in <module> str(v_dict['code']) + "'), " UnicodeEncodeError: 'ascii' codec can't encode character u'\xf4' in position 35: ordinal not in range(128) Why is Python even using ASCII? I thought it used UTF-8 by default, and this is a UTF-8 file. What is the problem?

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• Good Silverlight 4.0 chart / graph component?

  - by Duncan Bayne

  I've been using the Silverlight Toolkit but I'm finding the quality lacking; in particular this memory leak / phantom point bug renders the Chart component completely unusable. Can anyone recommend a good chart / graph component for Silverlight 4.0? I'm looking for one that provides: multiple simultaneous series, both scatter and line multi-select of points configurable tool-tips automatic axis scaling real-time update of data That last point sounds trivial but is tripping up the Silverlight Toolkit Chart; if you rapidly change the axis range, it sometimes leaves phantom points behind in addition to the points it should be displaying.

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• Using stringstream instead of `sscanf` to parse a fixed-format string

  - by John Dibling

  I would like to use the facilities provided by stringstream to extract values from a fixed-format string as a type-safe alternative to sscanf. How can I do this? Consider the following specific use case. I have a std::string in the following fixed format: YYYYMMDDHHMMSSmmm Where: YYYY = 4 digits representing the year MM = 2 digits representing the month ('0' padded to 2 characters) DD = 2 digits representing the day ('0' padded to 2 characters) HH = 2 digits representing the hour ('0' padded to 2 characters) MM = 2 digits representing the minute ('0' padded to 2 characters) SS = 2 digits representing the second ('0' padded to 2 characters) mmm = 3 digits representing the milliseconds ('0' padded to 3 characters) Previously I was doing something along these lines: string s = "20101220110651184"; unsigned year = 0, month = 0, day = 0, hour = 0, minute = 0, second = 0, milli = 0; sscanf(s.c_str(), "%4u%2u%2u%2u%2u%2u%3u", &year, &month, &day, &hour, &minute, &second, &milli ); The width values are magic numbers, and that's ok. I'd like to use streams to extract these values and convert them to unsigneds in the interest of type safety. But when I try this: stringstream ss; ss << "20101220110651184"; ss >> setw(4) >> year; year retains the value 0. It should be 2010. How do I do what I'm trying to do? I can't use Boost or any other 3rd party library, nor can I use C++0x.

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• how to draw a Bitmap to a Canvas with a variable alpha

  - by steelbytes

  Hi, I'm trying to draw a Bitmap to a Canvas with a variable amount of alpha. But I only get nothing (when alpha<255) or the 'full' bitmap (when alpha==255). Have also tried loading as a Drawable, and using drawable.setAlpha, but that gave the same result. my init BitmapFactory.Options opts = new BitmapFactory.Options(); opts.inScaled = false; opts.inSampleSize = 1; Bitmap img = BitmapFactory.decodeResource(getResources(),R.drawable.sample,opts); my onDraw() Paint p = new Paint(Paint.ANTI_ALIAS_FLAG|Paint.FILTER_BITMAP_FLAG); p.setColor((alpha<<24)+0xffffff); // alpha in range 0..255 canvas.drawBitmap(img, null, imgRect, p);

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• Alternative to "assign to a function call" in a python

  - by Pythonista's Apprentice

  I'm trying to solve this newbie puzzle: I've created this function: def bucket_loop(htable, key): bucket = hashtable_get_bucket(htable, key) for entry in bucket: if entry[0] == key: return entry[1] else: return None And I have to call it in two other functions (bellow) in the following way: to change the value of the element entry[1] or to append to this list (entry) a new element. But I can't do that calling the function bucket_loop the way I did because "you can't assign to function call" (assigning to a function call is illegal in Python). What is the alternative (most similar to the code I wrote) to do this (bucket_loop(htable, key) = value and hashtable_get_bucket(htable, key).append([key, value]))? def hashtable_update(htable, key, value): if bucket_loop(htable, key) != None: bucket_loop(htable, key) = value else: hashtable_get_bucket(htable, key).append([key, value]) def hashtable_lookup(htable, key): return bucket_loop(htable, key) Thanks, in advance, for any help! This is the rest of the code to make this script works: def make_hashtable(size): table = [] for unused in range(0, size): table.append([]) return table def hash_string(s, size): h = 0 for c in s: h = h + ord(c) return h % size def hashtable_get_bucket(htable, key): return htable[hash_string(key, len(htable))] Similar question (but didn't help me): Python: Cannot Assign Function Call

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• Vim: replacing start and end of a visual char, line or block

  - by gattu marrudu

  I am trying to find a shortcut to place a custom comment sequence on my code, e.g.: /* start of comment blah end of comment /**/ (it is easier to void the comment by just adding a / to the beginning) I would like to do this in Vim by selecting a visual line, block or char and adding '/' characters at the beginning of the block and '/*/' at the end, plus newlines. After selecting some lines (Shift-V) I tried this: '<,'>s/\(.*\)/\/*\r\1\r\/**\// But it adds the comment chars at EACH newline. How can I only apply the substitution at the beginning and end of the selected range? Thanks gm

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• Have you ever derived a programming solution from nature?

  - by Ryu

  When you step back and look at ... the nature of animals, insects, plants and the problems they have organically solved perhaps even the nature and balance of the universe Have you ever been able to solve a problem by deriving an approach from nature? I've heard of Ant Colony Algorithms being able to optimize supply chain amongst other things. Also Fractal's being the "geometry of nature" have been applied to a wide range of problems. Now that spring is here again and the world is coming back to life I'm wondering if anybody has some experiences they can share. Thanks PS I would recommend watching the "Hunting the Hidden Dimension" Nova episode on fractals.

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• avmutablecomposition insertEmptyTimeRange

  - by smartfaceweb

  I have created an avmutablecomposition and tried to use insertEmptyTimeRange to generate 1 minute of silence. This doesn't appear to be working. I have also tried creating an avmutablecompositiontrack using addMutableTrackWithMediaType:preferredTrackID: and then insertEmptyTimeRange on the track and still no success. To give some background on my app, I allow users to add audio samples a timeline and then playback or export and this is working really well using the av classes. The problem is that I need to make sure that the audio is exactly 1 min (for example). Regardless of the info about my specific app above, is it possible to insert an empty time range into a comp or comptrack?

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• what are the recent dataStructure and algorithms that one should know?

  - by Shamik

  Recently I came across the SkipList data structure. It really helped me to solve one otherwise critical problem to be solved. I was struggling to solve the same problem with Balanced Binary tree but it became very complex as the tree needs to be always balanced and I wanted to know the existence of not only a particular value but values in certain range. SkipList helped me to solve that problem effectively. I am wondering what else data structures that I need to know? I know - Array, List, Stack, Queue, Linked List, hashtable, tree and its different forms like B-tree, Trie etc. Would like to know if you find some other data structure/concept very interesting to know yet effective enough to be used in a daily development cycle.

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• I'm an idiot/blind and I can't find why I'm getting a list index error. Care to take a look at these 20 or so lines?

  - by Meff

  Basically it's supposed to take a set of coordinates and return a list of coordinates of it's neighbors. However, when it hits here:if result[i][0] < 0 or result[i][0] >= board.dimensions: result.pop(i) when i is 2, it gives me an out of index error. I can manage to have it print result[2][0] but at the if statement it throws the errors. I have no clue how this is happening and if anyone could shed any light on this problem I'd be forever in debt. def neighborGen(row,col,board): """ returns lists of coords of neighbors, in order of up, down, left, right """ result = [] result.append([row-1 , col]) result.append([row+1 , col]) result.append([row , col-1]) result.append([row , col+1]) #prune off invalid neighbors (such as (0,-1), etc etc) for i in range(len(result)): if result[i][0] < 0 or result[i][0] >= board.dimensions: result.pop(i) if result[i][1] < 0 or result[i][1] >= board.dimensions: result.pop(i) return result

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• Python list comprehension overriding value

  - by Joschua

  Hi, folks have a look at the following piece of code, which shows a list comprehension.. >>> i = 6 >>> s = [i * i for i in range(100)] >>> print(i) When you execute the code example in Python 2.6 it prints 99, but when you execute it in Python 3.x it prints 6. What were the reason for changing the behaviour and why is the output 6 in Python 3.x? Thank you in advance!

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• Ranged integers in .NET (or C#)

  - by Mal Ross

  Am I being blind, or does the .NET framework not provide any kind of ranged integer class? That is, a type that would prevent you setting a value outside some given bounds that are not the full range of the basic data type. For example, an integer type that would restrict its values to between 1 and 100. Showing my age here, but back in '93, I remember using that sort of thing in Modula-2 (eeek!), but I've not seen explicit framework / language support for it since. Am I just missing something, or is it a case of "it's so simple to make your own that the framework doesn't bother"? Cheers.

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• jquery: show data after change event

  - by klox

  i have this code: <script> $("#mod").change(function() { var matches=str.match(/(EE|[EJU]).*(D)/i); $.ajax({ type="post", url="process.php", data="matches", cache=false, async=false, success= function(res){ $('#rslt').replaceWith("<div id='value'><h6>Tuner range is" + res + " .</h6></div>"); return this; } }); return false; }); </script> i want this code can show the result normally..where is my fault?

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• What is the point of heightmaps?

  - by Jake Petroules

  I've been pondering this question awhile now... many 3d engines support advanced terrain rendering using quadtrees, LOD... all the features you expect. But every engine I've seen loads height data from heightmaps... grayscale bitmaps. I just can't understand how this is useful - each point in a heightmap can have one of 256 values. But what if you wanted to model Mt. Everest? with detail of 1 meter, or even greater? That's far outside the range of 256. Of course I understand that you can implement your own terrain format to achieve this, but I just can't see why heightmaps are so widely used despite their great limitations.

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• Modifiers in Makefile rule's dependency list

  - by gnu_maker

  The problem is fairly simple. I am trying to write a rule, that given the name of the required file will be able to tailor its dependencies. Let's say I have two programs: calc_foo and calc_bar and they generate a file with output dependent on the parameter. My target would have a name 'target_*_*'; for example, 'target_foo_1' would be generated by running './calc_foo 1'. The question is, how to write a makefile that would generate outputs of the two programs for a range of parameters?

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• What Can A 'TreeDict' (Or Treemap) Be Used For In Practice?

  - by Seun Osewa

  I'm developing a 'TreeDict' class in Python. This is a basically a dict that allows you to retrieve its key-value pairs in sorted order, just like the Treemap collection class in Java. I've implemented some functionality based on the way unique indexes in relational databases can be used, e.g. functions to let you retrieve values corresponding to a range of keys, keys greater than, less than or equal to a particular value in sorted order, strings or tuples that have a specific prefix in sorted order, etc. Unfortunately, I can't think of any real life problem that will require a class like this. I suspect that the reason we don't have sorted dicts in Python is that in practice they aren't required often enough to be worth it, but I want to be proved wrong. Can you think of any specific applications of a 'TreeDict'? Any real life problem that would be best solved by this data structure? I just want to know for sure whether this is worth it.

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• idiomatic way to take groups of n items from a list in Python?

  - by Wang

  Given a list A = [1 2 3 4 5 6] Is there any idiomatic (Pythonic) way to iterate over it as though it were B = [(1, 2) (3, 4) (5, 6)] other than indexing? That feels like a holdover from C: for a1,a2 in [ (A[i], A[i+1]) for i in range(0, len(A), 2) ]: I can't help but feel there should be some clever hack using itertools or slicing or something. (Of course, two at a time is just an example; I'd like a solution that works for any n.) Edit: related http://stackoverflow.com/questions/1162592/iterate-over-a-string-2-or-n-characters-at-a-time-in-python but even the cleanest solution (accepted, using zip) doesn't generalize well to higher n without a list comprehension and *-notation.

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• How to stream an HttpResponse with Django

  - by muudscope

  I'm trying to get the 'hello world' of streaming responses working for Django (1.2). I figured out how to use a generator and the yield function. But the response still not streaming. I suspect there's a middleware that's mucking with it -- maybe ETAG calculator? But I'm not sure how to disable it. Can somebody please help? Here's the "hello world" of streaming that I have so far: def stream_response(request): resp = HttpResponse( stream_response_generator()) return resp def stream_response_generator(): for x in range(1,11): yield "%s\n" % x # Returns a chunk of the response to the browser time.sleep(1)

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• JQuery multiple-choice quiz script: how to ensure the correct answer is available?

  - by DavidR

  I have a function. I pass to it an object with a list of questions and answers. I generate a random number from a range equal to the number of questions in the object. The script check to see if that question has been asked, and if not, it asks it, the correct answer is then passed to a variable correct. I want to give 4 possible answers, each one randomly selected from the list of possible answers. I have this. I just want to know what is the best way to ensure that the correct answer is placed in the list. So far, this is what I have: it puts four answers into four targeted boxes. I want to ensure that the correct answer is in a randomly selected box. function getRandom(limit) { return Math.floor(Math.random() * limit ) } $("#answers > .answer").each(function(i){ r = getRandom(total_questions); $(this).text(answers[r]) });

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• Member function overloading/template specialization issue

  - by Ferruccio

  I've been trying to call the overloaded table::scan_index(std::string, ...) member function without success. For the sake of clarity, I have stripped out all non-relevant code. I have a class called table which has an overloaded/templated member function named scan_index() in order to handle strings as a special case. class table : boost::noncopyable { public: template <typename T> void scan_index(T val, std::function<bool (uint recno, T val)> callback) { // code } void scan_index(std::string val, std::function<bool (uint recno, std::string val)> callback) { // code } }; Then there is a hitlist class which has a number of templated member functions which call table::scan_index(T, ...) class hitlist { public: template <typename T> void eq(uint fieldno, T value) { table* index_table = db.get_index_table(fieldno); // code index_table->scan_index<T>(value, [&](uint recno, T n)->bool { // code }); } }; And, finally, the code which kicks it all off: hitlist hl; // code hl.eq<std::string>(*fieldno, p1.to_string()); The problem is that instead of calling table::scan_index(std::string, ...), it calls the templated version. I have tried using both overloading (as shown above) and a specialized function template (below), but nothing seems to work. After staring at this code for a few hours, I feel like I'm missing something obvious. Any ideas? template <> void scan_index<std::string>(std::string val, std::function<bool (uint recno, std::string val)> callback) { // code }

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• Rationale in selecting Hash Key type

  - by Amrish

  Guys, I have a data structure which has 25 distinct keys (integer) and a value. I have a list of these objects (say 50000) and I intend to use a hash table to store/retrieve them. I am planning to take one of these approaches. Create a integer hash from these 25 integer keys and store it on a hash table. (Yeah! I have some means to handle collisions) Make a string concatenation on the individual keys and use it as a hash key for the hash table. For example, if the key values are 1,2,4,6,7 then the hash key would be "12467". Assuming that I have a total of 50000 records each with 25 distinct keys and a value, then will my second approach be a overkill when it comes to the cost of string comparisons it needs to do to retrieve and insert a record? Some more information! Each bucket in the hash table is a balanced binary tree. I am using the boost library's hash_combine method to create the hash from the 25 keys.

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• Microphone input

  - by George

  I'm trying to build a gadget that detects pistol shots using Android. It's a part of a training aid for pistol shooters that tells how the shots are distributed in time and I use a HTC Tattoo for testing. I use the MediaRecorder and its getMaxAmplitude method to get the highest amplitude during the last 1/100 s but it does not work as expected; speech gives me values from getMaxAmplitude in the range from 0 to about 25000 while the pistol shots (or shouting!) only reaches about 15000. With a sampling frequency of 8kHz there should be some samples with considerably high level. Anyone who knows how these things work? Are there filters that are applied before registering the max amplitude. If so, is it hardware or software? Thanks, /George

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• iOS Development: Why isn't my try block catching the exception?

  - by BeachRunnerJoe

  Hi. I have an exception being thrown in my code, but when I wrap it in an try/catch block, it doesn't get caught. The NSLog statement is never called in the catch block. Here's the code... NSInteger quoteLength; [data getBytes:(void *)&quoteLength range:NSMakeRange(sizeof(messageType), sizeof(quoteLength))]; @try { //Debugger stack trace shows an NSException being thrown on this statement NSData *stringData = [data subdataWithRange:NSMakeRange(sizeof(messageType) + sizeof(quoteLength), [data length])]; NSString *quote = [[NSString alloc] initWithData:stringData encoding:NSUTF8StringEncoding]; NSLog(@"received quote: %@",quote); [quote release]; } @catch (NSException * e) { NSLog(@"Exception Raised: %@", [e reason]); } Why doesn't it get caught? Thanks so much!

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• AWK: is there some flag to ignore comments?

  - by HH

  Comment rows are counted in the NR. Is there some flag to ignore comments? How can you limit the range in AWK, not like piping | sed -e '1d', to ignore comment rows? Example $ awk '{sum+=$3} END {avg=sum/NR} END {print avg}' coriolis_data 0.885491 // WRONG divided by 11, should be by 10 $ cat coriolis_data #d-err-t-err-d2-err .105 0.005 0.9766 0.0001 0.595 0.005 .095 0.005 0.9963 0.0001 0.595 0.005 .115 0.005 0.9687 0.0001 0.595 0.005 .105 0.005 0.9693 0.0001 0.595 0.005 .095 0.005 0.9798 0.0001 0.595 0.005 .105 0.005 0.9798 0.0001 0.595 0.005 .095 0.005 0.9711 0.0001 0.595 0.005 .110 0.005 0.9640 0.0001 0.595 0.005 .105 0.005 0.9704 0.0001 0.595 0.005 .090 0.005 0.9644 0.0001 0.595 0.005

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• Compiler turning a string& into a basic_string<>&

  - by Shtong

  Hello I'm coming back to C++ after long years spent on other technologies and i'm stuck on some weird behavior when calling some methods taking std::string as parameters : An example of call : LocalNodeConfiguration *LocalNodeConfiguration::ReadFromFile(std::string & path) { // ... throw configuration_file_error(string("Configuration file empty"), path); // ... } When I compile I get this (I cropped file names for readability) : /usr/bin/g++ -g -I/home/shtong/Dev/OmegaNoc/build -I/usr/share/include/boost-1.41.0 -o CMakeFiles/OmegaNocInternals.dir/configuration/localNodeConfiguration.cxx.o -c /home/shtong/Dev/OmegaNoc/source/configuration/localNodeConfiguration.cxx .../localNodeConfiguration.cxx: In static member function ‘static OmegaNoc::LocalNodeConfiguration* OmegaNoc::LocalNodeConfiguration::ReadFromFile(std::string&)’: .../localNodeConfiguration.cxx:72: error: no matching function for call to ‘OmegaNoc::configuration_file_error::configuration_file_error(std::string, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)’ .../configurationManager.hxx:25: note: candidates are: OmegaNoc::configuration_file_error::configuration_file_error(std::string&, std::string&) .../configurationManager.hxx:22: note: OmegaNoc::configuration_file_error::configuration_file_error(const OmegaNoc::configuration_file_error&) So as I understand it, the compiler is considering that my path parameter turned into a basic_string at some point, thus not finding the constructor overload I want to use. But I don't really get why this transformation happened. Some search on the net suggested me to use g++ but I was already using it. So any other advice would be appreciated :) Thanks

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