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  • Django Class Views and Reverse Urls

    - by kalhartt
    I have a good many class based views that use reverse(name, args) to find urls and pass this to templates. However, the problem is class based views must be instantiated before urlpatterns can be defined. This means the class is instantiated while urlpatterns is empty leading to reverse throwing errors. I've been working around this by passing lambda: reverse(name, args) to my templates but surely there is a better solution. As a simple example the following fails with exception: ImproperlyConfigured at xxxx The included urlconf mysite.urls doesn't have any patterns in it mysite.urls from mysite.views import MyClassView urlpatterns = patterns('', url(r'^$' MyClassView.as_view(), name='home') ) views.py class MyClassView(View): def get(self, request): home_url = reverse('home') return render_to_response('home.html', {'home_url':home_url}, context_instance=RequestContext(request)) home.html <p><a href={{ home_url }}>Home</a></p> I'm currently working around the problem by forcing reverse to run on template rendering by changing views.py to class MyClassView(View): def get(self, request): home_url = lambda: reverse('home') return render_to_response('home.html', {'home_url':home_url}, context_instance=RequestContext(request)) and it works, but this is really ugly and surely there is a better way. So is there a way to use reverse in class based views but avoid the cyclic dependency of urlpatterns requiring view requiring reverse requiring urlpatterns...

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  • Create a delegate from a property getter or setter method

    - by thecoop
    To create a delegate from a method you can use the compile-safe syntax: private int Method() { ... } // and create the delegate to Method... Func<int> d = Method; A property is a wrapper around a getter and setter method, and I want to create a delegate to a property getter method. Something like public int Prop { get; set; } Func<int> d = Prop; // or... Func<int> d = Prop_get; Which doesn't work, unfortunately. I have to create a separate lambda method, which seems unnecessary when the setter method matches the delegate signature anyway: Func<int> d = () => Prop; In order to use the delegate method directly, I have to use nasty reflection, which isn't compile-safe: // something like this, not tested... MethodInfo m = GetType().GetProperty("Prop").GetGetMethod(); Func<int> d = (Func<int>)Delegate.CreateDelegate(typeof(Func<int>), m); Is there any way of creating a delegate on a property getting method directly in a compile-safe way, similar to creating a delegate on a normal method at the top, without needing to use an intermediate lambda method?

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  • Having problems with sqlDataReader

    - by Anthony
    I am using a sqlDataReader to get data and set it to session variables. The problem is it doesn't want to work with expressions. I can reference any other column in the table, but not the expressions. The SQL does work. The code is below. Thanks in advance, Anthony Using myConnectionCheck As New SqlConnection(myConnectionString) Dim myCommandCheck As New SqlCommand() myCommandCheck.Connection = myConnectionCheck myCommandCheck.CommandText = "SELECT Projects.Pro_Ver, Projects.Pro_Name, Projects.TL_Num, Projects.LP_Num, Projects.Dev_Num, Projects.Val_Num, Projects.Completed, Flow.Initiate_Date, Flow.Requirements, Flow.Req_Date, Flow.Dev_Review, Flow.Dev_Review_Date, Flow.Interface, Flow.Interface_Date, Flow.Approval, Flow.Approval_Date, Flow.Test_Plan, Flow.Test_Plan_Date, Flow.Dev_Start, Flow.Dev_Start_Date, Flow.Val_Start, Flow.Val_Start_Date, Flow.Val_Complete, Flow.Val_Complete_Date, Flow.Stage_Production, Flow.Stage_Production_Date, Flow.MKS, Flow.MKS_Date, Flow.DIET, Flow.DIET_Date, Flow.Closed, Flow.Closed_Date, Flow.Dev_End, Flow.Dev_End_Date, Users_1.Email AS Expr1, Users_2.Email AS Expr2, Users_3.Email AS Expr3, Users_4.Email AS Expr4, Users_4.FNAME, Users_3.FNAME AS Expr5, Users_2.FNAME AS Expr6, Users_1.FNAME AS Expr7 FROM Projects INNER JOIN Users AS Users_1 ON Projects.TL_Num = Users_1.PIN INNER JOIN Users AS Users_2 ON Projects.LP_Num = Users_2.PIN INNER JOIN Users AS Users_3 ON Projects.Dev_Num = Users_3.PIN INNER JOIN Users AS Users_4 ON Projects.Val_Num = Users_4.PIN INNER JOIN Flow ON Projects.id = Flow.Flow_Pro_Num WHERE id = " myCommandCheck.CommandText += QSid myConnectionCheck.Open() myCommandCheck.ExecuteNonQuery() Dim count As Int16 = myCommandCheck.ExecuteScalar If count = 1 Then Dim myDataReader As SqlDataReader myDataReader = myCommandCheck.ExecuteReader() While myDataReader.Read() Session("TL_email") = myDataReader("Expr1").ToString() Session("PE_email") = myDataReader("Expr2").ToString() Session("DEV_email") = myDataReader("Expr3").ToString() Session("VAL_email") = myDataReader("Expr4").ToString() Session("Project_Name") = myDataReader("Pro_Name").ToString() End While myDataReader.Close() End If End Using

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  • Use of const double for intermediate results

    - by Arne
    Hi, I a writing a Simulation program and wondering if the use of const double is of any use when storing intermediate results. Consider this snippet: double DoSomeCalculation(const AcModel &model) { (...) const double V = model.GetVelocity(); const double m = model.GetMass(); const double cos_gamma = cos(model.GetFlightPathAngleRad()); (...) return m*V*cos_gamma*Chi_dot; } Note that the sample is there only to illustrate -- it might not make to much sense from the engineering side of things. The motivation of storing for example cos_gamma in a variable is that this cosine is used many time in other expressions covered by (...) and I feel that the code gets more readable when using cos_gamma rather than cos(model.GetFlightPathAngleRad()) in various expressions. Now the actual is question is this: since I expect the cosine to be the same througout the code section and I actually created the thing only as a placeholder and for convenience I tend to declare it const. Is there a etablished opinion on wether this is good or bad practive or whether it might bite me in the end? Does a compiler make any use of this additional information or am I actually hindering the compiler from performing useful optimizations? Arne

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  • Extending EF4 SQL Generation

    - by Basiclife
    Hi, We're using EF4 in a fairly large system and occasionally run into problems due to EF4 being unable to convert certain expressions into SQL. At present, we either need to do some fancy footwork (DB/Code) or just accept the performance hit and allow the query to be executed in-memory. Needless to say neither of these is ideal and the hacks we've sometimes had to use reduce readability / maintainability. What we would ideally like is a way to extend the SQL generation capabilities of the EF4 SQL provider. Obviously there are some things like .Net method calls which will always have to be client-side but some functionality like date comparisons (eg Group by weeks in Linq to Entities ) should be do-able. I've Googled but perhaps I'm using the wrong terminology as all I get is information about the new features of EF4 SQL Generation. For such a flexible and extensible framework, I'd be surprised if this isn't possible. In my head, I'm imagining inheriting from the [SQL 2008] provider and extending it to handle additional expressions / similar in the expression tree it's given to convert to SQL. Any help/pointers appreciated. We're using VS2010 Ultimate, .Net 4 (non-client profile) and EF4. The app is in ASP.Net and is running in a 64-Bit environment in case it makes a difference.

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  • Joining the previous and next sentence using python

    - by JudoWill
    I'm trying to join a set of sentences contained in a list. I have a function which determines whether a sentence in worth saving. However, in order to keep the context of the sentence I need to also keep the sentence before and after it. In the edge cases, where its either the first or last sentence then, I'll just keep the sentence and its only neighbor. An example is best: ex_paragraph = ['The quick brown fox jumps over the fence.', 'Where there is another red fox.', 'They run off together.', 'They live hapily ever after.'] t1 = lambda x: x.startswith('Where') t2 = lambda x: x'startswith('The ') The result for t1 should be: ['The quick brown fox jumps over the fence. Where there is another red fox. They run off together.'] The result for t2 should be: ['The quick brown fox jumps over the fence. Where there is another red fox.'] My solution is: def YieldContext(sent_list, cont_fun): def JoinSent(sent_list, ind): if ind == 0: return sent_list[ind]+sent_list[ind+1] elif ind == len(sent_list)-1: return sent_list[ind-1]+sent_list[ind] else: return ' '.join(sent_list[ind-1:ind+1]) for sent, sentnum in izip(sent_list, count(0)): if cont_fun(sent): yield JoinSent(sent_list, sent_num) Does anyone know a "cleaner" or more pythonic way to do something like this. The if-elif-else seems a little forced. Thanks, Will PS. I'm obviously doing this with a more complicated "context-function" but this is just for a simple example.

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  • In languages which create a new scope each time in a loop block, a new local copy of the local loop

    - by Jian Lin
    It seems that in language like C, Java, and Ruby (as opposed to Javascript), a new scope is created for each iteration of a loop block, and the local variable defined for the loop is actually made into a local variable every single time and recorded in this new scope? For example, in Ruby: p RUBY_VERSION $foo = [] (1..5).each do |i| $foo[i] = lambda { p i } end (1..5).each do |j| $foo[j].call() end the print out is: [MacBook01:~] $ ruby scope.rb "1.8.6" 1 2 3 4 5 [MacBook01:~] $ So, it looks like when a new scope is created, a new local copy of i is also created and recorded in this new scope, so that when the function is executed at a later time, the "i" is found in those scope chains as 1, 2, 3, 4, 5 respectively. Is this true? (It sounds like a heavy operation). Contrast that with p RUBY_VERSION $foo = [] i = 0 (1..5).each do |i| $foo[i] = lambda { p i } end (1..5).each do |j| $foo[j].call() end This time, the i is defined before entering the loop, so Ruby 1.8.6 will not put this i in the new scope created for the loop block, and therefore when the i is looked up in the scope chain, it always refer to the i that was in the outside scope, and give 5 every time: [MacBook01:~] $ ruby scope2.rb "1.8.6" 5 5 5 5 5 [MacBook01:~] $ I heard that in Ruby 1.9, i will be treated as a local defined for the loop even when there is an i defined earlier? The operation of creating a new scope, creating a new local copy of i each time through the loop seems heavy, as it seems it wouldn't have matter if we are not invoking the functions at a later time. So when the functions don't need to be invoked at a later time, could the interpreter and the compiler to C / Java try to optimize it so that there is not local copy of i each time?

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  • Complex derived attributes in Django models

    - by rabidpebble
    What I want to do is implement submission scoring for a site with users voting on the content, much like in e.g. reddit (see the 'hot' function in http://code.reddit.com/browser/sql/functions.sql). My submission model currently keeps track of up and down vote totals. Currently, when a user votes I create and save a related Vote object and then use F() expressions to update the Submission object's voting totals. The problem is that I want to update the score for the submission at the same time, but F() expressions are limited to only simple operations (it's missing support for log(), date_part(), sign() etc.) From my limited experience with Django I can see 4 options here: extend F() somehow (haven't looked at the code yet) to support the missing SQL functions; this is my preferred option and seems to fit within the Django framework the best define a scoring function (much like reddit's 'hot' function) in my database, and have Django use the value of that function for the value of the score field; as far as I can tell, #2 is not possible wrap my two step voting process in a suitably isolated transaction so that I can calculate the voting totals in Python and then update the Submission's voting totals without fear that another vote against the submission could be added/changed in the meantime; I'm hesitant to take this route because it seems overly complex - what is a "suitably isolated transaction" in this case anyway? use raw SQL; I would prefer to avoid this entirely -- what's the point of an ORM if I have to revert to SQL for such a common use case as this! (Note that this coming from somebody who loves sprocs, but is using Django for ease of development.) Before I embark on this mission to extend F() (which I'm not sure is even possible), am I about to reinvent the wheel? Is there a more standard way to do this? It seems like such a common use case and yet in an hour of searching I have yet to find a common solution...

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  • Can this code be further optimized??

    - by kaki
    i understand that the code given below will not be compltely understood unless i explain my whole of previous and next lines of code. But this is part of the code which is causing so much of delay in my project and want to optimize this. i want to know which code part is faulty and how could this be replaced. i guess,few can say that use of this function is heavy compared and other ligher method are available to do this work please help, thanks in advance for i in range(len(lists)): save=database_index[lists[i]] #print save #if save[1]!='text0194'and save[1]!='text0526': using_data[save[0]]=save p=os.path.join("c:/begpython/wavnk/",str(str(str(save[1]).replace('phone','text'))+'.pm')) x1=open(p , 'r') x2=open(p ,'r') for i in range(6): x1.readline() x2.readline() gen = (float(line.partition(' ')[0]) for line in x1) r= min(enumerate(gen), key=lambda x: abs(x[1] - float(save[4]))) #print r[0] a1=linecache.getline(str(str(p).replace('.pm','.mcep')), (r[0]+1)) #print a1 p1=str(str(a1).rstrip('\n')).split(' ') #print p1 join_cost_index_end[save[0]]=p1 #print join_cost_index_end gen = (float(line.partition(' ')[0]) for line in x2) r= min(enumerate(gen), key=lambda x: abs(x[1] - float(save[3]))) #print r[0] a2=linecache.getline(str(str(p).replace('.pm','.mcep')), (r[0]+1)) #print a2 p2=str(str(a2).rstrip('\n')).split(' ') #print p2 join_cost_index_strt[save[0]]=p2 #print join_cost_index_strt j=j+1 #print j #print join_cost_index_end #print join_cost_index_strt enter code here here my database_index has about 2,50,000 entries`

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  • python histogram one-liner

    - by mykhal
    there are many ways, how to code histogram in Python. by histogram, i mean function, counting objects in an interable, resulting in the count table (i.e. dict). e.g.: >>> L = 'abracadabra' >>> histogram(L) {'a': 5, 'b': 2, 'c': 1, 'd': 1, 'r': 2} it can be written like this: def histogram(L): d = {} for x in L: if x in d: d[x] += 1 else: d[x] = 1 return d ..however, there are much less ways, how do this in a single expression. if we had "dict comprehensions" in python, we would write: >>> { x: L.count(x) for x in set(L) } but we don't have them, so we have to write: >>> dict([(x, L.count(x)) for x in set(L)]) however, this approach may yet be readable, but is not efficient - L is walked-through multiple times, so this won't work for single-life generators.. the function should iterate well also through gen(), where: def gen(): for x in L: yield x we can go with reduce (R.I.P.): >>> reduce(lambda d,x: dict(d, x=d.get(x,0)+1), L, {}) # wrong! oops, does not work, the key name is 'x', not x :( i ended with: >>> reduce(lambda d,x: dict(d.items() + [(x, d.get(x, 0)+1)]), L, {}) (in py3k, we would have to write list(d.items()) instead of d.items(), but it's hypothethical, since there is no reduce there) please beat me with a better one-liner, more readable! ;)

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  • C# reflection instantiation

    - by NickLarsen
    I am currently trying to create a generic instance factory for which takes an interface as the generic parameter (enforced in the constructor) and then lets you get instantiated objects which implement that interface from all types in all loaded assemblies. The current implementation is as follows:     public class InstantiationFactory     {         protected Type Type { get; set; }         public InstantiationFactory()         {             this.Type = typeof(T);             if (!this.Type.IsInterface)             {                 // is there a more descriptive exception to throw?                 throw new ArgumentException(/* Crafty message */);             }         }         public IEnumerable GetLoadedTypes()         {             // this line of code found in other stack overflow questions             var types = AppDomain.CurrentDomain.GetAssemblies()                 .SelectMany(a = a.GetTypes())                 .Where(/* lambda to identify instantiable types which implement this interface */);             return types;         }         public IEnumerable GetImplementations(IEnumerable types)         {             var implementations = types.Where(/* lambda to identify instantiable types which implement this interface */                 .Select(x = CreateInstance(x));             return implementations;         }         public IEnumerable GetLoadedImplementations()         {             var loadedTypes = GetLoadedTypes();             var implementations = GetImplementations(loadedTypes);             return implementations;         }         private T CreateInstance(Type type)         {             T instance = default(T);             var constructor = type.GetConstructor(Type.EmptyTypes);             if (/* valid to instantiate test */)             {                 object constructed = constructor.Invoke(null);                 instance = (T)constructed;             }             return instance;         }     } It seems useful to me to have my CreateInstance(Type) function implemented as an extension method so I can reuse it later and simplify the code of my factory, but I can't figure out how to return a strongly typed value from that extension method. I realize I could just return an object:     public static class TypeExtensions     {         public object CreateInstance(this Type type)         {             var constructor = type.GetConstructor(Type.EmptyTypes);             return /* valid to instantiate test */ ? constructor.Invoke(null) : null;         }     } Is it possible to have an extension method create a signature per instance of the type it extends? My perfect code would be this, which avoids having to cast the result of the call to CreateInstance():     Type type = typeof(MyParameterlessConstructorImplementingType);     MyParameterlessConstructorImplementingType usable = type.CreateInstance();

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  • Targeted Simplify in Mathematica

    - by Timo
    I generate very long and complex analytic expressions of the general form: (...something not so complex...)(...ditto...)(...ditto...)...lots... When I try to use Simplify, Mathematica grinds to a halt, I am assuming due to the fact that it tries to expand the brackets and or simplify across different brackets. The brackets, while containing long expressions, are easily simplified by Mathematica on their own. Is there some way I can limit the scope of Simplify to a single bracket at a time? Edit: Some additional info and progress. So using the advice from you guys I have now started using something in the vein of In[1]:= trouble = Log[(x + I y) (x - I y) + Sqrt[(a + I b) (a - I b)]]; In[2]:= Replace[trouble, form_ /; (Head[form] == Times) :> Simplify[form],{3}] Out[2]= Log[Sqrt[a^2 + b^2] + (x - I y) (x + I y)] Changing Times to an appropriate head like Plus or Power makes it possible to target the simplification quite accurately. The problem / question that remains, though, is the following: Simplify will still descend deeper than the level specified to Replace, e.g. In[3]:= Replace[trouble, form_ /; (Head[form] == Plus) :> Simplify[form], {1}] Out[3]= Log[Sqrt[a^2 + b^2] + x^2 + y^2] simplifies the square root as well. My plan was to iteratively use Replace from the bottom up one level at a time, but this clearly will result in vast amount of repeated work by Simplify and ultimately result in the exact same bogging down of Mathematica I experienced in the outset. Is there a way to restrict Simplify to a certain level(s)? I realize that this sort of restriction may not produce optimal results, but the idea here is getting something that is "good enough".

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  • Methods and properties in scheme - is object oriented programming possible in scheme?

    - by incrediman
    I will use a simple example to illustrate my question. In Java, C, or any other OOP language, I could create a pie class in a way similar to this: class Apple{ public String flavor; public int pieces; private int tastiness; public goodness(){ return tastiness*pieces; } } What's the best way to do that with Scheme? I suppose I could do with something like this: (define make-pie (lambda (flavor pieces tastiness) (list flavor pieces tastiness))) (define pie-goodness (lambda (pie) (* (list-ref pie 1) (list-ref pie 2)))) (pie-goodness (make-pie 'cherry 2 5)) ;output: 10 ...where cherry is the flavor, 2 is the pieces, and 5 is the tastiness. However then there's no type-safety or visibility, and everything's just shoved in an unlabeled list. How can I improve that? Sidenote: The make-pie procedure expects 3 arguments. If I want to make some of them optional (like I'd be able to in curly-brace languages like Java or C), is it good practice to just take the arguments in as a list (that is treat the arguments as a list - not require one argument which is a list) and deal with them that way?

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  • Exiting from the Middle of an Expression Without Using Exceptions

    - by Jon Purdy
    Is there a way to emulate the use of flow-control constructs in the middle of an expression? Is it possible, in a comma-delimited expression x, y, for y to cause a return? Edit: I'm working on a compiler for something rather similar to a functional language, and the target language is C++. Everything is an expression in the source language, and the sanest, simplest translation to the destination language leaves as many things expressions as possible. Basically, semicolons in the target language become C++ commas. In-language flow-control constructs have presented no problems thus far; it's only return. I just need a way to prematurely exit a comma-delimited expression, and I'd prefer not to use exceptions unless someone can show me that they don't have excessive overhead in this situation. The problem of course is that most flow-control constructs are not legal expressions in C++. The only solution I've found so far is something like this: try { return x(), // x(); (1 ? throw Return(0) : 0); // return 0; } catch (Return& ret) { return ref.value; } The return statement is always there (in the event that a Return construct is not reached), and as such the throw has to be wrapped in ?: to get the compiler to shut up about its void result being used in an expression. I would really like to avoid using exceptions for flow control, unless in this case it can be shown that no particular overhead is incurred; does throwing an exception cause unwinding or anything here? This code needs to run with reasonable efficiency. I just need a function-level equivalent of exit().

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  • (x86) Assembler Optimization

    - by Pindatjuh
    I'm building a compiler/assembler/linker in Java for the x86-32 (IA32) processor targeting Windows. High-level concepts of a "language" (in essential a Java API for creating executables) are translated into opcodes, which then are wrapped and outputted to a file. The translation process has several phases, one is the translation between languages: the highest-level code is translated into the medium-level code which is then translated into the lowest-level code (probably more than 3 levels). My problem is the following; if I have higher-level code (X and Y) translated to lower-level code (x, y, U and V), then an example of such a translation is, in pseudo-code: x + U(f) // generated by X + V(f) + y // generated by Y (An easy example) where V is the opposite of U (compare with a stack push as U and a pop as V). This needs to be 'optimized' into: x + y (essentially removing the "useless" code) My idea was to use regular expressions. For the above case, it'll be a regular expression looking like this: x:(U(x)+V(x)):null, meaning for all x find U(x) followed by V(x) and replace by null. Imagine more complex regular expressions, for more complex optimizations. This should work on all levels. What do you suggest? What would be a good approach to optimize in these situations?

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  • Return Double from Boost thread

    - by Benedikt Wutzi
    Hi I have an Boost thread which should return a double. The function looks like this: void analyser::findup(const double startwl, const double max, double &myret){ this->data.begin(); for(int i = (int)data.size() ; i >= 0;i--){ if(this->data[i].lambda > startwl){ if(this->data[i].db >= (max-30)) { myret = this->data[i+1].lambda; std::cout <<"in thread " << myret << std::endl; return; } } } } this function is called by another function: void analyser::start_find_up(const double startwl, const double max){ double tmp = -42.0; boost::thread up(&analyser::findup,*this, startwl,max,tmp); std::cout << "before join " << tmp << std::endl; up.join(); std::cout << "after join " << tmp << std::endl; } Anyway I've tried and googled almost anything but i can't get it to return a value. The output looks like this right now. before join -42 in thread 843.487 after join -42 Thanks for any help.

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  • Javascript string replace with calculations

    - by Chris
    Is there a way to resolve mathematical expressions in strings in javascript? For example, suppose I want to produce the string "Tom has 2 apples, Lucy has 3 apples. Together they have 5 apples" but I want to be able to substitute in the variables. I can do this with a string replacement: string = "Tom has X apples, Lucy has Y apples. Together they have Z apples"; string2 = string.replace(/X/, '2').replace(/Y/, '3').replace(/Z/, '5'); However, it would be better if, instead of having a variable Z, I could use X+Y. Now, I could also do a string replace for X+Y and replace it with the correct value, but that would become messy when trying to deal with all the possible in-string calculations I might want to do. I suppose I'm looking for a way to achieve this: string = "Something [X], something [Y]. Something [(X+Y^2)/5X]"; And for the [_] parts to be understood as expressions to be resolved before substituting back into the string. Thanks for your help.

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  • Parsing every part of an HTTP header field-value

    - by brickner
    Hi all. I'm parsing HTTP data directly from packets (either TCP reconstructed or not, you can assume it is). I'm looking for the best way to parse HTTP as accurately as possible. The main issue here is the HTTP header. Looking at the basic RFC of HTTP/1.1, it seems that HTTP header parsing would be complex. The RFC describes very complex regular expressions for different parts of the header. Should I write these regular expressions to parse the different parts of the HTTP header? The basic parsing I've written so far for HTTP header is for the generic HTTP header: message-header = field-name ":" [ field-value ] And I've included replacing inner LWS with SP and repeating headers with the same field-name with comma separated values as described in section 4.2. However, looking at section 14.9 for example would show that in order to parse the different parts of the field-value I need a much more complex parsing scheme. How do you suggest I should handle the complex parts of HTTP parsing (specifically the field-value) assuming I want to give the parser users the full capabilities of HTTP and to parse every part of HTTP? Design suggestions for this would also be appreciated. Thanks.

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  • Dynamic Method Creation

    - by TJMonk15
    So, I have been trying to research this all morning, and have had no luck. I am trying to find a way to dynamically create a method/delegate/lambda that returns a new instance of a certain class (not known until runtime) that inherits from a certain base class. I can guarantee the following about the unknown/dynamic class It will always inherit from one known Class (Row) It will have atleast 2 constructors (one accepting a long, and one accepting an IDataRecord) I plan on doign the following: Finding all classes that have a certain attribute on them Creating a delegate/method/lambda/whatever that creates a new instance of the class Storing the delegate/whatever along with some properties in a struct/class Insert the struct into a hashtable When needed, pull the info out of the hashtable and calling the delegate/whatever to get a new instance of the class and returning it/adding it to a list/etc. I need help only with #2 above!!! I have no idea where to start. I really just need some reference material to get me started, or some keywords to throw into google. This is for a compact/simple to use ORM for our office here. I understand the above is not simple, but once working, should make maintaining the code incredibly simple. Please let me know if you need any more info! And thanks in advance! :)

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  • Django repeating vars/cache issue?

    - by Mark
    I'm trying to build a better/more powerful form class for Django. It's working well, except for these sub-forms. Actually, it works perfectly right after I re-start apache, but after I refresh the page a few times, my HTML output starts to look like this: <input class="text" type="text" id="pickup_addr-pickup_addr-pickup_addr-id-pickup_addr-venue" value="" name="pickup_addr-pickup_addr-pickup_addr-pickup_addr-venue" /> The pickup_addr- part starts repeating many times. I was looking for loops around the prefix code that might have cause this to happen, but the output isn't even consistent when I refresh the page, so I think something is getting cached somewhere, but I can't even imagine how that's possible. The prefix car should be reset when the class is initialized, no? Unless it's somehow not initializing something? class Form(object): count = 0 def __init__(self, data={}, prefix='', action='', id=None, multiple=False): self.fields = {} self.subforms = {} self.data = {} self.action = action self.id = fnn(id, 'form%d' % Form.count) self.errors = [] self.valid = True if not empty(prefix) and prefix[-1:] not in ('-','_'): prefix += '-' for name, field in inspect.getmembers(self, lambda m: isinstance(m, Field)): if name[:2] == '__': continue field_name = fnn(field.name, name) field.label = fnn(field.label, humanize(field_name)) field.name = field.widget.name = prefix + field_name + ife(multiple, '[]') field.id = field.auto_id = field.widget.id = ife(field.id==None, 'id-') + prefix + fnn(field.id, field_name) + ife(multiple, Form.count) field.errors = [] val = fnn(field.widget.get_value(data), field.default) if isinstance(val, basestring): try: val = field.coerce(field.format(val)) except Exception, err: self.valid = False field.errors.append(escape_html(err)) field.val = self.data[name] = field.widget.val = val for rule in field.rules: rule.fields = self.fields rule.val = field.val rule.name = field.name self.fields[name] = field for name, form in inspect.getmembers(self, lambda m: ispropersubclass(m, Form)): if name[:2] == '__': continue self.subforms[name] = self.__dict__[name] = form(data=data, prefix='%s%s-' % (prefix, name)) Form.count += 1 Let me know if you need more code... I know it's a lot, but I just can't figure out what's causing this!

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  • Help me write my LISP :) LISP environments, Ruby Hashes...

    - by MikeC8
    I'm implementing a rudimentary version of LISP in Ruby just in order to familiarize myself with some concepts. I'm basing my implementation off of Peter Norvig's Lispy (http://norvig.com/lispy.html). There's something I'm missing here though, and I'd appreciate some help... He subclasses Python's dict as follows: class Env(dict): "An environment: a dict of {'var':val} pairs, with an outer Env." def __init__(self, parms=(), args=(), outer=None): self.update(zip(parms,args)) self.outer = outer def find(self, var): "Find the innermost Env where var appears." return self if var in self else self.outer.find(var) He then goes on to explain why he does this rather than just using a dict. However, for some reason, his explanation keeps passing in through my eyes and out through the back of my head. Why not use a dict, and then inside the eval function, when a new "sub-environment" needs to be created, just take the existing dict and update the key/value pairs that need to be updated, and pass that new dict into the next eval? Won't the Python interpreter keep track of the previous "outer" envs? And won't the nature of the recursion ensure that the values are pulled out from "inner" to "outer"? I'm using Ruby, and I tried to implement things this way. Something's not working though, and it might be because of this, or perhaps not. Here's my eval function, env being a regular Hash: def eval(x, env = $global_env) ........ elsif x[0] == "lambda" then ->(*args) { eval(x[2], env.merge(Hash[*x[1].zip(args).flatten(1)])) } ........ end The line that matters of course is the "lambda" one. If there is a difference, what's importantly different between what I'm doing here and what Norvig did with his Env class? If there's no difference, then perhaps someone can enlighten me as to why Norvig uses the Env class. Thanks :)

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  • emacs lisp mapcar doesn't apply function to all elements?

    - by Stephen
    Hi, I have a function that takes a list and replaces some elements. I have constructed it as a closure so that the free variable cannot be modified outside of the function. (defun transform (elems) (lexical-let ( (elems elems) ) (lambda (seq) (let (e) (while (setq e (car elems)) (setf (nth e seq) e) (setq elems (cdr elems))) seq)))) I call this on a list of lists. (defun tester (seq-list) (let ( (elems '(1 3 5)) ) (mapcar (transform elems) seq-list))) => ((10 1 8 3 6 5 4 3 2 1) ("a" "b" "c" "d" "e" "f")) It does not seem to apply the function to the second element of the list provided to tester(). However, if I explicitly apply this function to the individual elements, it works... (defun tester (seq-list) (let ( (elems '(1 3 5)) ) (list (funcall (transform elems) (car seq-list)) (funcall (transform elems) (cadr seq-list))))) => ((10 1 8 3 6 5 4 3 2 1) ("a" 1 "c" 3 "e" 5)) If I write a simple function using the same concepts as above, mapcar seems to work... What could I be doing wrong? (defun transform (x) (lexical-let ( (x x) ) (lambda (y) (+ x y)))) (defun tester (seq) (let ( (x 1) ) (mapcar (transform x) seq))) (tester (list 1 3)) => (2 4) Thanks

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  • Problem with circular definition in Scheme

    - by user8472
    I am currently working through SICP using Guile as my primary language for the exercises. I have found a strange behavior while implementing the exercises in chapter 3.5. I have reproduced this behavior using Guile 1.4, Guile 1.8.6 and Guile 1.8.7 on a variety of platforms and am certain it is not specific to my setup. This code works fine (and computes e): (define y (integral (delay dy) 1 0.001)) (define dy (stream-map (lambda (x) x) y)) (stream-ref y 1000) The following code should give an identical result: (define (solve f y0 dt) (define y (integral (delay dy) y0 dt)) (define dy (stream-map f y)) y) (solve (lambda (x) x) 1 0.001) But it yields the error message: standard input:7:14: While evaluating arguments to stream-map in expression (stream-map f y): standard input:7:14: Unbound variable: y ABORT: (unbound-variable) So when embedded in a procedure definition, the (define y ...) does not work, whereas outside the procedure in the global environment at the REPL it works fine. What am I doing wrong here? I can post the auxiliary code (i.e., the definitions of integral, stream-map etc.) if necessary, too. With the exception of the system-dependent code for cons-stream, they are all in the book. My own implementation of cons-stream for Guile is as follows: (define-macro (cons-stream a b) `(cons ,a (delay ,b)))

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  • Regular expression, excluding .. in suffix of email addy

    - by user1754700
    This is homework, I've been working on it for a while, I've done lots of reading and feel I have gotten pretty familiar with regex for a beginner. I am trying to find a regular expression for validating/invalidating a list of emails. There are two addresses which are giving me problems, I can't get them both to validate the correct way at the same time. I've gone through a dozen different expressions that work for all the other emails on the list but I can't get those two at the same time. First, the addresses. [email protected] - invalid [email protected] - valid The part of my expression which validates the suffix I originally started with @.+\\.[[a-z]0-9]+ And had a second pattern for checking some more invalid addresses and checked the email against both patterns, one checked for validity the other invalidity but my professor said he wanted it all in on expression. @[[\\w]+\\.[\\w]+]+ or @[\\w]+\\.[\\w]+ I've tried it written many, many different ways but I'm pretty sure I was just using different syntax to express these two expressions. I know what I want it to do, I want it to match a character class of "character+"."character+"+ The plus sign being at least one. It works for the invalid class when I only allow the character class to repeat one time(and obviously the ip doesn't get matched), but when I allow the character class to repeat itself it matches the second period even thought it isn't preceded by a character. I don't understand why.

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  • Macro and array crossing

    - by Thomas
    I am having a problem with a lisp macro. I would like to create a macro which generate a switch case according to an array. Here is the code to generate the switch-case: (defun split-elem(val) `(,(car val) ',(cdr val))) (defmacro generate-switch-case (var opts) `(case ,var ,(mapcar #'split-elem opts))) I can use it with a code like this: (generate-switch-case onevar ((a . A) (b . B))) But when I try to do something like this: (defparameter *operators* '((+ . OPERATOR-PLUS) (- . OPERATOR-MINUS) (/ . OPERATOR-DIVIDE) (= . OPERATOR-EQUAL) (* . OPERATOR-MULT))) (defmacro tokenize (data ops) (let ((sym (string->list data))) (mapcan (lambda (x) (generate-switch-case x ops)) sym))) (tokenize data *operators*) I got this error: *** - MAPCAR: A proper list must not end with OPS. But I don't understand why. When I print the type of ops I get SYMBOL I was expecting CONS, is it related? Also, for my function tokenize how many times the lambda is evaluated (or the macro expanded)?

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