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  • Derivative of a Higher-Order Function

    - by Claudiu
    This is in the context of Automatic Differentiation - what would such a system do with a function like map, or filter - or even one of the SKI Combinators? Example: I have the following function: def func(x): return sum(map(lambda a: a**x, range(20))) What would its derivative be? What will an AD system yield as a result? (This function is well-defined on real-number inputs).

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  • Hidden features of C#3.5 [closed]

    - by xyz
    Possible Duplicate: Hidden Features of C#? Kindly donot mistake this question with Hidden Features of C#?. It is specific to C# 3.5 / dot net 3.5 I have figured out some(what I have used so far). They are as under 1) Linq 2(Objects, Sql, Xml) 2) Lambda expressions 3) Extention methods 4) Object initializers 5) Collection initialisers 6) Anonymous delegates 7)Automatic properties Please help me in finding out more. Thanks

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  • architecture python question

    - by tom smith
    hi. creating a distributed crawling python app. it consists of a master server, and associated client apps that will run on client servers. the purpose of the client app is to run across a targeted site, to extract specific data. the clients need to go "deep" within the site, behind multiple levels of forms, so each client is specifically geared towards a given site. each client app looks something like main: parse initial url call function level1 (data1) function level1 (data) parse the url, for data1 use the required xpath to get the dom elements call the next function call level2 (data) function level2 (data2) parse the url, for data2 use the required xpath to get the dom elements call the next function call level3 function level3 (dat3) parse the url, for data3 use the required xpath to get the dom elements call the next function call level4 function level4 (data) parse the url, for data4 use the required xpath to get the dom elements at the final function.. --all the data output, and eventually returned to the server --at this point the data has elements from each function... my question: given that the number of calls that is made to the child function by the current function varies, i'm trying to figure out the best approach. each function essentialy fetches a page of content, and then parses the page using a number of different XPath expressions, combined with different regex expressions depending on the site/page. if i run a client on a single box, as a sequential process, it'll take awhile, but the load on the box is rather small. i've thought of attempting to implement the child functions as threads from the current function, but that could be a nightmare, as well as quickly bring the "box" to its knees! i've thought of breaking the app up in a manner that would allow the master to essentially pass packets to the client boxes, in a way to allow each client/function to be run directly from the master. this process requires a bit of rewrite, but it has a number of advantages. a bunch of redundancy, and speed. it would detect if a section of the process was crashing and restart from that point. but not sure if it would be any faster... i'm writing the parsing scripts in python.. so... any thoughts/comments would be appreciated... i can get into a great deal more detail, but didn't want to bore anyone!! thanks! tom

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  • Ignoring Whitespace with Regex(perl)

    - by Zerobu
    Hello, I am using Perl Regular expressions. How would i go about ignoring white space and still perform a test to see if a string match. For example. $var = " hello "; #I want var to igonore whitespace and still match if($var =~ m/hello/) { }

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  • Difference between generator expression and generator function

    - by Neil G
    Is there any difference — performance or otherwise — between generator expressions and generator functions? In [1]: def f(): ...: yield from range(4) ...: In [2]: def g(): ...: return (i for i in range(4)) ...: In [3]: f() Out[3]: <generator object f at 0x109902550> In [4]: list(f()) Out[4]: [0, 1, 2, 3] In [5]: list(g()) Out[5]: [0, 1, 2, 3] In [6]: g() Out[6]: <generator object <genexpr> at 0x1099056e0>

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  • T-SQL String Functions: difference between using Left/Right and Substring and strange behaviour

    - by TheObserver
    I am using SQL Server 2008 & 2005 (Express). I'm trying to extract part of an alpha numeric string from a varchar field. RIGHT(str_field,3) yields null values but substring(str_field, len(str_field)-2, len(str_field)) gives the right value. left(str_field,7) gives the expected values. What gives? I would have thought that RIGHT(str_field,3) and substring(str_field, len(str_field)-2, len(str_field)) are equivalent expressions.

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  • Rails: three most recent comments with unique users

    - by Dennis Collective
    what would I put in the named scope :by_unique_users so that I can do Comment.recent.by_unique_users.limit(3), and only get one comment per user? class User has_many :comments end class Comment belongs_to :user named_scope :recent, :order => 'comments.created_at DESC' named_scope :limit, lambda { |limit| {:limit => limit}} named_scope :by_unique_users end on sqlite named_scope :by_unique_user, :group = "user_id" works, but makes it freak out on postgres, which is deployed on production PGError: ERROR: column "comments.id" must appear in the GROUP BY clause or be used in an aggregate function

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  • Need Flex Regex Validation Expression for password that allows for only alphanumeric values and requ

    - by BlueDude
    Hi I'm trying to setup a RegexpValidator that only accepts a string of alphanumeric characters between 6-30 characters long and requires one number. I'm new to Regular Expressions and everything I've tried seems to keep returning an invalid ValidationRsultEvent. Here's a chunk of code: <mx:RegExpValidator id="regexValidator" source="{passwordInput}" property="text" triggerEvent="" valid="onPasswordValidate(event)" invalid="onPasswordValidate(event)" /> private function validateRegister():void { regexValidator.expression = "^(?=.*(\d|\W)).{6,30}$"; regexValidator.validate(); }

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  • Using two struts2 taglibs in each other

    - by Milad.KH
    Hi I want to use two struts taglib in each other, something like this: < s:properties value="url-< s:properties value="number"/"/ or < s:properties value="url-${number}"/ but I got the following error in the second one: According to TLD or attribute directive in tag file, attribute values does not accept any expressions. Anybody has a solution ? Thanks

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  • Built-in precedence in Expression Trees?

    - by jdk
    I'm unable to find the .NET FCL built-in concept of precedence to leverage while constructing Expression Trees. Ref System.Linq.Expressions Namespace. Is this something that must be handled manually in code, or is it somehow implicit and I'm not recognizing it? Maybe through helper methods or classes? I want to apply it to math operations to ensure 3 + 5 * 10 results in 53 instead of 80.

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  • Regex to use each letter only once?

    - by gtcaz
    Is it possible to construct a PCRE-style regular expression that will only match each letter in a list only once? For example, if you have the letters "lrsa" and you try matching a word list against: ^[lrsa]*m[lrsa]*$ you're going to match "lams" (valid), but also "lamas" (invalid for our purposes because you only had one "a"). If your letter set was "lrsaa", you would want to match "lamas". Is this possible with regular expressions, or should I handle it programmatically?

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  • wildcards to use in codeigniter routing?

    - by ajsie
    in codeigniter you can use wildcard to reroute. i never heard the word wildcards before. is this a set of rules you can use like regexp? cause in codeigniter documentation they just gave some examples eg. $route['product/(:num)'] = "catalog/product_lookup_by_id/$1"; is there a list/reference with all the available wildcard expressions you can use?

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  • regular expression help

    - by JPro
    I always get confused using regular expressions. Can anyone please suggest me a tutorial? I need help with checking for a string which, cannot contain any wild characters except colon, comma, full stop. It will be better to replace these if found. Any help? Thanks.

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  • Using Squeak from a shell

    - by Vijay Mathew
    Can I launch Squeak as a REPL (no GUI), where I can enter and evaluate Smalltalk expressions? I know the default image don't allow this. Is there any documentation on how to build a minimum image that can be accessed from a command-line shell?

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  • Getting started with nbehave

    - by dotnetdev
    Hi, I am looking at using BDD, however, when evaluating the stories/conditions I write (using nBehave), how do I check if the story passes? Do I write another library with test methods? For example, if I want to test a site for having a link called "About", do I write a method which can check this and then another method in another class library which can call the method to check the link via lambda syntax and add the relevant test and bdd attributes? Thanks

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  • Code hot swapping in Erlang

    - by Roger Alsing
    I recently saw a video about Erlang on InfoQ, In that video one of the creators presented how to replace the behavior of a message loop. He was simply sending a message containing a lambda of the new version of the message loop code, which then was invoked instead of calling the old loop again. Is that code hot swapping in Erlang reffers to? Or is that some other more native feature?

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  • How to test if a gawk string contain a number?

    - by Tim Menzies
    In gawk I know two ways to test if a string contains a number. Which is best? Method one: using regular expressions: function method1(x) { return x ~ /^[+-]?([0-9]+[.]?[0-9]*|[.][0-9]+)([eE][+-]?[0-9]+)?$/ } Method two: the coercion trick (simpler): function method2(x) { return (x != "") && (x+0 == x) } Is there any reason to favor the more complex method1 over the simpler method2?

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  • SED: Matching on 2 patterns on the same line

    - by Brian Knott
    Hi I want to delete a line using sed if it matches 2 regular expressions in the same line. EG the line starts with /* and end with */ (comment). The following script will do most of that. sed -e '/^\/*/ d' -e '/*\/$/ d' filename This script will remove all lines that start with * and end with */. I want it to remove the line only if is meets both criteria not one.

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  • Parse HTML with CSS or XPath selectors?

    - by ovolko
    My goal is to parse HTML with lxml, which supports both XPath and CSS selectors. I can tie my model properties either to CSS or XPath, but I'm not sure which one would be the best, e.g. less fuss when HTML layout is changed, simpler expressions, greater extraction speed. What would you choose in such a situation?

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