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  • executing named_scoped only when there are present params

    - by Luca Romagnoli
    Hi have a model like this: class EventDate < ActiveRecord::Base belongs_to :event named_scope :named, lambda { | name | { :joins => { :event => :core}, :conditions => ["name like ?", "%#{ name }%"] }} named_scope :date_range, lambda { | start, length | { :conditions => ["day >= ? AND day <= ?", start, date + (length || 30) ] }} it works correctly if i launch name = "ba" start = Date.today EventDate.named(name).date_range(start , start + 2) But if the name or the start is nil i don't want execute the named_scope like name = nil EventDate.named(name).date_range(start , start + 2) Is possible to set a condition inner the named_scope ? thanks

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  • How do you sort files numerically?

    - by Zachary Young
    Hello all, First off, I'm posting this because when I was looking for a solution to the problem below, I could not find one on stackoverflow. So, I'm hoping to add a little bit to the knowledge base here. I need to process some files in a directory and need the files to be sorted numerically. I found some examples on sorting--specifically with using the lamba pattern--at wiki.python.org, and I put this together: #!env/python import re tiffFiles = """ayurveda_1.tif ayurveda_11.tif ayurveda_13.tif ayurveda_2.tif ayurveda_20.tif ayurveda_22.tif""".split('\n') numPattern = re.compile('_(\d{1,2})\.', re.IGNORECASE) tiffFiles.sort(cmp, key=lambda tFile: int(numPattern.search(tFile).group(1))) print tiffFiles I'm still rather new to Python and would like to ask the community if there are any improvements that can be made to this: shortening the code up (removing lambda), performance, style/readability? Thank you, Zachary

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  • Using Python tuples as vectors

    - by Etaoin
    I need to represent immutable vectors in Python ("vectors" as in linear algebra, not as in programming). The tuple seems like an obvious choice. The trouble is when I need to implement things like addition and scalar multiplication. If a and b are vectors, and c is a number, the best I can think of is this: tuple(map(lambda x,y: x + y, a, b)) # add vectors 'a' and 'b' tuple(map(lambda x: x * c, a)) # multiply vector 'a' by scalar 'c' which seems inelegant; there should be a clearer, simpler way to get this done -- not to mention avoiding the call to tuple, since map returns a list. Is there a better option?

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  • web2py error while using distinct in the queries

    - by Steve
    Hi, I am using web2py with GAE. While using some of the queries which has a distinct clause, GAE throws out an error.I have pasted the Traceback. Can someone please help me out with this. In FILE: /base/data/home/apps/panneersoda/1.341206242889687944/applications/init/controllers/default.py Traceback (most recent call last): File "/base/data/home/apps/panneersoda/1.341206242889687944/gluon/restricted.py", line 173, in restricted exec ccode in environment File "/base/data/home/apps/panneersoda/1.341206242889687944/applications/init/controllers/default.py:profileview", line 263, in <module> File "/base/data/home/apps/panneersoda/1.341206242889687944/gluon/globals.py", line 96, in <lambda> self._caller = lambda f: f() File "/base/data/home/apps/panneersoda/1.341206242889687944/applications/init/controllers/default.py:profileview", line 97, in profileview File "/base/data/home/apps/panneersoda/1.341206242889687944/gluon/contrib/gql.py", line 675, in select (items, tablename, fields) = self._select(*fields, **attributes) File "/base/data/home/apps/panneersoda/1.341206242889687944/gluon/contrib/gql.py", line 624, in _select raise SyntaxError, 'invalid select attribute: %s' % key SyntaxError: invalid select attribute: distinct Thanks

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  • Consolidating coding styles: Funcs, private method, single method classes

    - by jdoig
    Hi all, We currently have 3 devs with, some, conflicting styles and I'm looking for a way to bring peace to the kingdom... The Coders: Foo 1: Likes to use Func's & Action's inside public methods. He uses actions to alias off lengthy method calls and Func's to perform simple tasks that can be expressed in 1 or 2 lines and will be used frequently through out the code Pros: The main body of his code is succinct and very readable, often with only one or 2 public methods per class and rarely any private methods. Cons: The start of methods contain blocks of lambda rich code that other developers don't enjoy reading; and, on occasion, can contain higher order functions that other dev's REALLY don't like reading. Foo 2: Likes to create a private method for (almost) everything the public method will have to do . Pros: Public methods remain small and readable (to all developers). Cons: Private methods are numerous. With private methods that call into other private methods, that call into... etc, etc. Making code hard to navigate. Foo 3: Likes to create a public class with a, single, public method for every, non-trivial, task that needs performing, then dependency inject them into other objects. Pros: Easily testable, easy to understand (one object, one responsibility). Cons: project gets littered by classes, opening multiple class files to understand what code does makes navigation awkward. It would be great to take the best of all these techniques... Foo-1 Has really nice, readable (almost dsl-like) code... for the most part, except for all the Action and Func lambda shenanigans bulked together at the start of a method. Foo-3 Has highly testable and extensible code that just feels a bit "belt-&-braces" for some solutions and has some code-navigation niggles (constantly hitting F12 in VS and opening 5 other .cs files to find out what a single method does). And Foo-2... Well I'm not sure I like anything about the one-huge .cs file with 2 public methods and 12 private ones, except for the fact it's easier for juniors to dig into. I admit I grossly over-simplified the explanations of those coding styles; but if any one knows of any patterns, practices or diplomatic-manoeuvres that can help unite our three developers (without just telling any of them to just "stop it!") that would be great. From a feasibility standpoint : Foo-1's style meets with the most resistance due to some developers finding lambda and/or Func's hard to read. Foo-2's style meets with a less resistance as it's just so easy to fall into. Foo-3's style requires the most forward thinking and is difficult to enforce when time is short. Any ideas on some coding styles or conventions that can make this work?

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  • How can this closure test be written in other languages?

    - by Jian Lin
    I wonder how the following closure test can be written in other languages, such as C and Java. Can the same result be expected also in Perl, Python, and PHP? Ideally, we don't need to make a new local variable such as x and assign it the value of i inside the loop, but just so that i has a new copy in the new scope each time. (if possible). (some discussion is in this question.) The following is in Ruby, the "1.8.6" on the first line of result is the Ruby version which can be ignored. 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:~] $ Contrast that with another test, with i defined outside: 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 the print out: [MacBook01:~] $ ruby scope2.rb "1.8.6" 5 5 5 5 5 [MacBook01:~] $

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  • Expression.OrElse, dynamically creating a condition.

    - by Jim
    Hi, I am attempting to create a dynamic where clause using the standard expression API. var query = ( from p in Parties orderby p.PartyId orderby p.FullName select p ).AsQueryable(); Expression<Func<Party, bool>> @fn = (p) => SqlMethods.Like(p.FullName, "%smith%") || SqlMethods.Like(p.Person.FirstName, "%smith%"); Expression<Func<Party, bool>> @sn = (p) => SqlMethods.Like(p.Person.FirstName, words[0]); ParameterExpression pe = Expression.Parameter(typeof(Party), "p"); Expression orelse = Expression.OrElse( Expression.Lambda(@fn, pe), Expression.Lambda(@sn, pe) ); The expressions above will ultimately be added to a where clause. I need to add a bunch of 'likes'. How do I do this? I get InvalidOperationException on the operator OrElse I have also tried Expression.Or Thanks Regards Craig.

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  • Why does Scala apply thunks automatically, sometimes?

    - by Anonymouse
    At just after 2:40 in ShadowofCatron's Scala Tutorial 3 video, it's pointed out that the parentheses following the name of a thunk are optional. "Buh?" said my functional programming brain, since the value of a function and the value it evaluates to when applied are completely different things. So I wrote the following to try this out. My thought process is described in the comments. object Main { var counter: Int = 10 def f(): Int = { counter = counter + 1; counter } def runThunk(t: () => Int): Int = { t() } def main(args: Array[String]): Unit = { val a = f() // I expect this to mean "apply f to no args" println(a) // and apparently it does val b = f // I expect this to mean "the value f", a function value println(b) // but it's the value it evaluates to when applied to no args println(b) // and the evaluation happens immediately, not in the call runThunk(b) // This is an error: it's not println doing something funny runThunk(f) // Not an error: seems to be val doing something funny } }   To be clear about the problem, this Scheme program (and the console dump which follows) shows what I expected the Scala program to do. (define counter (list 10)) (define f (lambda () (set-car! counter (+ (car counter) 1)) (car counter))) (define runThunk (lambda (t) (t))) (define main (lambda args (let ((a (f)) (b f)) (display a) (newline) (display b) (newline) (display b) (newline) (runThunk b) (runThunk f)))) > (main) 11 #<procedure:f> #<procedure:f> 13   After coming to this site to ask about this, I came across this answer which told me how to fix the above Scala program: val b = f _ // Hey Scala, I mean f, not f() But the underscore 'hint' is only needed sometimes. When I call runThunk(f), no hint is required. But when I 'alias' f to b with a val then apply it, it doesn't work: the evaluation happens in the val; and even lazy val works this way, so it's not the point of evaluation causing this behaviour.   That all leaves me with the question: Why does Scala sometimes automatically apply thunks when evaluating them? Is it, as I suspect, type inference? And if so, shouldn't a type system stay out of the language's semantics? Is this a good idea? Do Scala programmers apply thunks rather than refer to their values so much more often that making the parens optional is better overall? Examples written using Scala 2.8.0RC3, DrScheme 4.0.1 in R5RS.

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  • E4X in ActionScript

    - by Brian Genisio
    Hey all, Looking at the E4X implementation in ActionScript, it occurs to me that they had to figure out how to do three things that I am not sure can be done within ActionScript regularly: Properties/Getters prefixed with @: var myAttribute = xmlPerson.@name; Nameless functions for filtering: xmlData.person.(/* predicate */) lambda syntax for predicates: xmlData.person.(@name == "Brian") So here is my question: Are these just one-off capabilities (much like Vector.<>) they put in just for E4X, therefore keeping out of reach for us? Or do we, as ActionScript developers, have access to these features? More specifically, I'd love to get access to the expression tree of that lambda predicate for my own code (not tied to the XML classes in any way). I figured out that this is called the "filter operator"... but I am not sure how to harness it. Not sure I can... since ActionScript does not allow for operator overloading :(

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  • Aquamacs and IDLWAVE

    - by nicolavianello
    I've just installed the new Aquamacs 2.0 in my Mac Os X 10.6.3 and I'm an happy user of IDLWAVE on Aquamacs for programming in IDL. Unfortunately I run into a problem which I can't understand. I used in my configuration file to put the following (setq idlwave-surround-by-blank t) for the beautiful space around operator. This used to work till Aquamacs 2.0 preview b3 (third beta release) from that on, it stops to work and every time I type an operator (the same for '=' '<' '' etc) I got the following message Debugger entered--Lisp error: (void-variable idlwave-expand-equal) (lambda nil (interactive) (self-insert-command 1) idlwave-expand- equal -1 -1)() call-interactively((lambda nil (interactive) (self-insert-command 1) idlwave-expand-equal -1 -1) nil nil) Any help is welcommed

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  • Calling a method with getattr in Python

    - by brain_damage
    How to call a method using getattr? I want to create a metaclass, which can call non-existing methods of some other class that start with the word 'oposite_'. The method should have the same number of arguments, but to return the opposite result. def oposite(func): return lambda s, *args, **kw: not oposite(s, *args, **kw) class Negate(type): def __getattr__(self, name): if name.startswith('oposite_'): return oposite(self.__getattr__(name[8:])) def __init__(self,*args,**kwargs): self.__getattr__ = Negate.__getattr__ class P(metaclass=Negate): def yep(self): return True But the problem is that self.__getattr__(sth) returns a NoneType object. >>> p = P() >>> p.oposite_yep() Traceback (most recent call last): File "<pyshell#115>", line 1, in <module> p.oposite_yep() TypeError: <lambda>() takes at least 1 positional argument (0 given) How to deal with this?

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  • Function Composition in C++

    - by Channel72
    There are a lot of impressive Boost libraries such as Boost.Lambda or Boost.Phoenix which go a long way towards making C++ into a truly functional language. But is there a straightforward way to create a composite function from any 2 or more arbitrary functions or functors? If I have: int f(int x) and int g(int x), I want to do something like f . g which would statically generate a new function object equivalent to f(g(x)). This seems to be possible through various techniques, such as those discussed here. Certainly, you can chain calls to boost::lambda::bind to create a composite functor. But is there anything in Boost which easily allows you to take any 2 or more functions or function objects and combine them to create a single composite functor, similar to how you would do it in a language like Haskell?

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  • Dynamic Operator Overloading on dict classes in Python

    - by Ishpeck
    I have a class that dynamically overloads basic arithmetic operators like so... import operator class IshyNum: def __init__(self, n): self.num=n self.buildArith() def arithmetic(self, other, o): return o(self.num, other) def buildArith(self): map(lambda o: setattr(self, "__%s__"%o,lambda f: self.arithmetic(f, getattr(operator, o))), ["add", "sub", "mul", "div"]) if __name__=="__main__": number=IshyNum(5) print number+5 print number/2 print number*3 print number-3 But if I change the class to inherit from the dictionary (class IshyNum(dict):) it doesn't work. I need to explicitly def __add__(self, other) or whatever in order for this to work. Why?

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  • Flymake quits right ahead after loading with js2-mode

    - by artistoex
    When opening .js files, js2-mode and, subsequently, flymake-js is automatically loaded. But flymake unloads right ahead with the message Toggling flymake-mode off; better pass an explicit argument. However, when enabling it manually, using M-x flymake-mode, it keeps activated. Has anybody encountered similar behavior and has fixed it? My setup: I followed the instructions on emacswiki to set up Flymake to work with the most recent js2-mode with a little modification: (add-hook 'js2-mode-hook '(lambda () (flymake-js-load))) instead of (add-hook 'javascript-mode-hook '(lambda () (flymake-js-load)))

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  • Closure and nested lambdas in C++0x

    - by DanDan
    Using C++0x, how do I capture a variable when I have a lambda within a lambda? For example: std::vector<int> c1; int v = 10; <--- I want to capture this variable std::for_each( c1.begin(), c1.end(), [v](int num) <--- This is fine... { std::vector<int> c2; std::for_each( c2.begin(), c2.end(), [v](int num) <--- error on this line, how do I recapture v? { // Do something }); });

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  • Converting ObjC Blocks to C# Lambas

    - by Sam
    I need some help converting an Objective-C block to C#. Here is the source ObjC: NSDate* addYear = [_calendar dateByAddingComponents:((^{ NSDateComponents* components = [NSDateComponents new]; components.month = 12; return components; })()) toDate:now options:0]; Now I tried the following in C#: NSDate date = _calendar.DateByAddingComponents((() => { NSDateComponents components = new NSDateComponents(); components.Month = 12; return components; })(), now, NSCalendarOptions.None); To which I get the following compiler error: Expression denotes a 'anonymous method' where a 'method group' was expected. Removing the parentheses around the lambda yields Cannot convert 'lambda expression' to non-delegate type 'MonoTouch.Foundation.NSDateComponents'. What is the correct C# syntax? I need to retain the closures as there are a lot more in the code base that I am porting.

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  • Instance_eval: why the class of subclass is superclass

    - by Raj
    def singleton_class class << self self end end class Human proc = lambda { puts 'proc says my class is ' + self.name.to_s } singleton_class.instance_eval do define_method(:lab) do proc.call end end end class Developer < Human end Human.lab # class is Human Developer.lab # class is Human ; oops Following solution works. def singleton_class class << self self end end class Human proc = lambda { puts 'proc says my class is ' + self.name.to_s } singleton_class.instance_eval do define_method(:lab) do self.instance_eval &proc end end end class Developer < Human end Human.lab # class is Human Developer.lab # class is Human ; oops Why Developer.lab is reporting that it is Human ? And what can be done so that proc reports Developer when Developer.lab is invoked.

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  • python multiprocessing.Process.Manager not producing consistent results?

    - by COpython
    I've written the following code to illustrate the problem I'm seeing. I'm trying to use a Process.Manager.list() to keep track of a list and increment random indices of that list. Each time there are 100 processes spawned, and each process increments a random index of the list by 1. Therefore, one would expect the SUM of the resulting list to be the same each time, correct? I get something between 203 and 205. from multiprocessing import Process, Manager import random class MyProc(Process): def __init__(self, A): Process.__init__(self) self.A = A def run(self): i = random.randint(0, len(self.A)-1) self.A[i] = self.A[i] + 1 if __name__ == '__main__': procs = [] M = Manager() a = M.list(range(15)) print('A: {0}'.format(a)) print('sum(A) = {0}'.format(sum(a))) for i in range(100): procs.append(MyProc(a)) map(lambda x: x.start(), procs) map(lambda x: x.join(), procs) print('A: {0}'.format(a)) print('sum(A) = {0}'.format(sum(a)))

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  • Programmatic binding of accelerators in wxPython

    - by Inductiveload
    I am trying to programmatically create and bind a table of accelerators in wxPython in a loop so that I don't need to worry about getting and assigning new IDs to each accelerators (and with a view to inhaling the handler list from some external resource, rather than hard-coding them). I also pass in some arguments to the handler via a lambda since a lot of my handlers will be the same but with different parameters (move, zoom, etc). The class is subclassed from wx.Frame and setup_accelerators() is called during initialisation. def setup_accelerators(self): bindings = [ (wx.ACCEL_CTRL, wx.WXK_UP, self.on_move, 'up'), (wx.ACCEL_CTRL, wx.WXK_DOWN, self.on_move, 'down'), (wx.ACCEL_CTRL, wx.WXK_LEFT, self.on_move, 'left'), (wx.ACCEL_CTRL, wx.WXK_RIGHT, self.on_move, 'right'), ] accelEntries = [] for binding in bindings: eventId = wx.NewId() accelEntries.append( (binding[0], binding[1], eventId) ) self.Bind(wx.EVT_MENU, lambda event: binding[2](event, binding[3]), id=eventId) accelTable = wx.AcceleratorTable(accelEntries) self.SetAcceleratorTable(accelTable) def on_move(self, e, direction): print direction However, this appears to bind all the accelerators to the last entry, so that Ctrl+Up prints "right", as do all the other three. How to correctly bind multiple handlers in this way?

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  • How do I do this in Python (File Manipulation)?

    - by ThinkCode
    I have a bunch of HTML files in HTML folder. Those HTML files have unicode characters which I solved by using filter(lambda x: x in string.printable, line). Now how do I write the changes back to the original file? What is the best way of doing it? Each HTML file is of 30 kb in size. 1 import os, string 2 3 for file in os.listdir("HTML/"): 4 print file 5 myfile = open('HTML/' + file) 6 fileList = myfile.readlines() 9 for line in fileList: 10 #print line 11 line = filter(lambda x: x in string.printable, line) 12 myfile.close()

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  • Is OOP based on any branch of mathematics?

    - by ektrules
    I know relational databases are based on set-theory, functional programming is based on lambda calculus, logic programming is based on logic (of course :)), and now that I think of it; I'm not sure if imperative and generic programming is based on any particular branch of mathematics either.

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  • Remote debug a linux app from XCode

    - by erick2red
    hey guys: it's simple i had this linux pc which i connect remote and i have this application that i run there and i want to debug it, but i just don't know how. It's the simpler c++ app on the world, load some libraries, do some calculus, print some output and return, It's just that, i just haven't any clue. So any help would be appreciated. Thxs anyway

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