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• ActiveRecord and transactionsin between `before_save` and `save`

  - by JP

  I have some logic in before_save whereby (only) when some conditions are met I let the new row be created with special_number equal to the maximum special_number in the database + 1. (If the conditions aren't met then I do something different, so I can't use auto-increments) My worry is that two threads acting on this database at once might pick the same special_number if the second is executed while the first is saving. Is there way to lock the database between before_save and finishing the save, but only in some cases? I know all saves are sent in transactions, will this do the job for me? def before_save if things_are_just_right # -- Issue some kind of lock? # -- self.lock? I have no idea # Pick new special_number new_special = self.class.maximum('special_number') + 1 write_attribute('special_number',new_special) else # No need to lock in this case write_attribute('special_number',some_other_number) end end

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• Can I reproduce Scala's behavior for == ?

  - by JPP

  In Programming in Scala, I can read that the == operator behaves as if it was defined like this: final def == (that: Any): Boolean = if (null eq this) {null eq that} else {this equals that} But there must actually be compiler magic to avoid null pointer exceptions, right? Is there any way for me to replicate this behavior with pure Scala; i.e., have an operator/method return one thing if the receiver is null and another one if it isn't? What I mean is an actual implementation of null eq this. I suppose I can write a "pimp" and then define the method on the wrapper class, but is there a more direct way to do this?

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• How to add values accordingly of the first indices of a dictionary of tuples of a list of strings? Python 3x

  - by TheStruggler

  I'm stuck on how to formulate this problem properly and the following is: What if we had the following values: {('A','B','C','D'):3, ('A','C','B','D'):2, ('B','D','C','A'):4, ('D','C','B','A'):3, ('C','B','A','D'):1, ('C','D','A','B'):1} When we sum up the first place values: [5,4,2,3] (5 people picked for A first, 4 people picked for B first, and so on like A = 5, B = 4, C = 2, D = 3) The maximum values for any alphabet is 5, which isn't a majority (5/14 is less than half), where 14 is the sum of total values. So we remove the alphabet with the fewest first place picks. Which in this case is C. I want to return a dictionary where {'A':5, 'B':4, 'C':2, 'D':3} without importing anything. This is my work: def popular(letter): '''(dict of {tuple of (str, str, str, str): int}) -> dict of {str:int} ''' my_dictionary = {} counter = 0 for (alphabet, picks) in letter.items(): if (alphabet[0]): my_dictionary[alphabet[0]] = picks else: my_dictionary[alphabet[0]] = counter return my_dictionary This returns duplicate of keys which I cannot get rid of. Thanks.

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• app engine's back referencing is too slow. How can I make it faster?

  - by Ray Yun

  Google app engine has smart feature named back references and I usually iterate them where the traditional SQL's computed column need to be used. Just imagine that need to accumulate specific force's total hp. class Force(db.Model): hp = db.IntegerProperty() class UnitGroup(db.Model): force = db.ReferenceProperty(reference_class=Force,collection_name="groups") hp = db.IntegerProperty() class Unit(db.Model): group = db.ReferenceProperty(reference_class=UnitGroup,collection_name="units") hp = db.IntegerProperty() When I code like following, it was horribly slow (almost 3s) with 20 forces with single group - single unit. (I guess back-referencing force reload sub entities. Am I right?) def get_hp(self): hp = 0 for group in self.groups: group_hp = 0 for unit in group.units: group_hp += unit.hp hp += group_hp return hp How can I optimize this code? Please consider that there are more properties should be computed for each force/unit-groups and I don't want to save these collective properties to each entities. :)

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• Python - alternative to list.remove(x)?

  - by Seafoid

  Hi, I wish to compare two lists. Generally this is not a problem as I usually use a nested for loop and append the intersection to a new list. In this case, I need to delete the intersection of A and B from A. A = [['ab', 'cd', 'ef', '0', '567'], ['ghy5'], ['pop', 'eye']] B = [['ab'], ['hi'], ['op'], ['ej']] My objective is to compare A and B and delete A intersection B from A, i.e., delete A[0][0] in this case. I tried: def match(): for i in A: for j in i: for k in B: for v in k: if j == v: A.remove(j) list.remove(x) throws a ValueError.

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• Multiple HTTP request - Rails

  - by bradleyg

  My application checks a number of domains to see if they are valid (approx 100). I have the following code to check a single domain: def self.test_url uri, limit = 10 if limit == 0 return get_error_messages("001") end begin url = URI.parse(uri) response = Net::HTTP.start(url.host, url.port).request_head('/') rescue SocketError => e return get_error_messages("002") end case response when Net::HTTPRedirection then test_url(response['location'], limit - 1) else return get_error_messages(response.code) end end The code checks for the response code while taking into account redirects. This works fine. The only problem I have is when I put this in a loop I want it to run in parallel. So I don't have to wait for domain 1 to respond before I can request domain 2. I have managed this in PHP using curl_multi to run the requests in parallel. Is there a similar thing I can do in Rails?

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• String contains all the elements of a list

  - by CSSS

  I am shifting to Python, and am still relatively new to the pythonic approach. I want to write a function that takes a string and a list and returns true if all the elements in the list occur in the string. This seemed fairly simple. However, I am facing some difficulties with it. The code goes something like this: def myfun(str,list): for a in list: if not a in str: return False return True Example : myfun('tomato',['t','o','m','a']) should return true myfun('potato',['t','o','m','a']) should return false myfun('tomato',['t','o','m']) should return true Also, I was hoping if someone could suggest a possible regex approach here. I am trying out my hands on them too.

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• Providing updates during a long Rails controller action

  - by highBandWidth

  I have an action that takes a long time. I want to be able to provide updates during the process so the user is not confused as to whether he lost the connection or something. Can I do something like this: class HeavyLiftingController < ApplicationController def data_mine render_update :js=>"alert('Just starting!')" # do some complicated find etc. render_update :js=>"alert('Found the records!')" # do some processing ... render_update :js=>"alert('Done processig')" # send @results to view end end

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• How to manually close connection in BaseHTTPServer?

  - by user1657188

  I have a script that sends a request to an HTTP server. HTTP server script (snippet): ... class MyHandler(BaseHTTPServer.BaseHTTPRequestHandler): def do_GET(sa): pdict = cgi.parse_header(sa.headers.getheader('referer')) q = pdict[0] q = urllib.unquote(q) if q == "enternetixplorer" # basically just ignore this, doesn't have to do with the question sa.wfile.write("blah blah blah") # now restart server httpd.server_close() python = sys.executable os.execl(python, python, * sys.argv) ... The "blah blah blah" is sent back, but the connection does not seem to close, and my script is waiting forever until I abort the server. (My thought is BaseHTTPServer automatically closes connection when the last part in "do_GET()" is computed, but I prevent this by restarting the script.) If I'm right, how do I close the connection? If not, what else might be the problem? Edit: The server script HAS to restart the entire program.

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• rreplace - How to replace the last occurence of an expression in a string

  - by Barthelemy

  Is there a quick way in Python to replace strings by starting from the end? For example: >>> def rreplace(old, new, occurence) >>> ... # Code to replace the last occurences of old by new >>> '<div><div>Hello</div></div>'.rreplace('</div>','</bad>',1) >>> '<div><div>Hello</div></bad>'

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• Minimizing calls to database in rails

  - by ming yeow

  Hi guys, i am familiar with memcached and eager loading, but neither seems to solve the problem i am facing. My main performance lag comes from hundreds of data retrieval calls from the database. The tricky thing is that I do not know which set of users i need to retrieve until i have several steps of computation. I can refactor my code, but i was wondering how you experts handle this situation? I think it should be a fairly common situation def newsfeed - find out which users i need - retrieve those users via DB - find out which events happened for these users - for each of those events - retrieve new set of users - find out which groups are relevant - for each of those groups - retrieve new set of users - etc, etc end

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• Django: optimizing queries

  - by Josh

  I want to list the number of items for each list. How can I find this number in a single query, rather than a query for each list? Here is a simplified version of my current template code: {% for list in lists %} <li> {{ listname }}: {% with list.num_items as item_count %} {{ item_count }} item{{ item_count|pluralize }} {% endwith %} </li> {% endfor %} lists is passed as: List.objects.filter(user=user) and num_items is a property of the List model: def _get_num_items(self): return self.item_set.filter(archived=False).count() num_items = property(_get_num_items) This queries SELECT COUNT(*) FROM "my_app_item" WHERE... n times, where n is the number of lists. Is it possible to make a single query here?

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• Converting time period strings to value/unit pair

  - by randomtoor

  I need to parse the contents of a string that represents a time period. The format of the string is value/unit, e.g.: 1s, 60min, 24h. I would separate the actual value (an int) and unit (a str) to separated variables. At the moment I do it like this: def validate_time(time): binsize = time.strip() unit = re.sub('[0-9]','',binsize) if unit not in ['s','m','min','h','l']: print "Error: unit {0} is not valid".format(unit) sys.exit(2) tmp = re.sub('[^0-9]','',binsize) try: value = int(tmp) except ValueError: print "Error: {0} is not valid".format(time) sys.exit(2) return value,unit However, it is not ideal as things like 1m0 are also (wrongly) validated (value=10,unit=m). What is the best way to validate/parse this input?

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• Is it valid to include view code in Model?

  - by Shreekumar S

  Guys I'm new to RoR and MVC. I've a model which deals with loan beneficiary's data. To access the structured data (including small piece of HTML data) I created a method like this class Beneficiary < ActiveRecord::Base   def info   "#{name}</br>#{age},#{sex}</br><b>Address :</b>#{address}"   end end And in the view, I'm using this info something like this <%= @b.info.html_safe %> were, b is an instance of Beneficiary class It's working fine for me. I just want to know that, Am i violating the MVC rule here? Is it valid to include view code in Model?

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• How do you pass self to class_eval in ruby?

  - by klochner

  I'm working on a metaprogramming task, where I'm trying to use a single method to define a polymorphic association in the calling class, while also defining the association in the target class. I need to pass in the name of the calling class to get the association right. Here's a snippet that should get the idea across: class SomeClass < ActiveRecord::Base has_many :join_models, :dependent=:destroy end class JoinModel < ActiveRecord::Base belongs_to :some_class belongs_to :entity, :polymorphic=true end module Foo module ClassMethods def acts_as_entity has_many :join_models, :as=:entity, :dependent=:destroy has_many :some_classes, :through=:join_models klass = self.name.tableize SomeClass.class_eval "has_many :#{klass}, :through=:join_models" end end end I'd like to eliminate the klass= line, but don't know how else to pass a reference to self from the calling class into class_eval. any suggestions?

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• How to optimize this script

  - by marks34

  I have written the following script. It opens a file, reads each line from it splitting by new line character and deleting first character in line. If line exists it's being added to array. Next each element of array is splitted by whitespace, sorted alphabetically and joined again. Every line is printed because script is fired from console and writes everything to file using standard output. I'd like to optimize this code to be more pythonic. Any ideas ? import sys def main(): filename = sys.argv[1] file = open(filename) arr = [] for line in file: line = line[1:].replace("\n", "") if line: arr.append(line) for line in arr: lines = line.split(" ") lines.sort(key=str.lower) line = ''.join(lines) print line if __name__ == '__main__': main()

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• Functional equivalent of if (p(f(a), f(b)) a else b

  - by oxbow_lakes

  I'm guessing that there must be a better functional way of expressing the following: def foo(i: Any) : Int if (foo(a) < foo(b)) a else b So in this example f == foo and p == _ < _. There's bound to be some masterful cleverness in scalaz for this! I can see that using BooleanW I can write: p(f(a), f(b)).option(a).getOrElse(b) But I was sure that I would be able to write some code which only referred to a and b once. If this exists it must be on some combination of Function1W and something else but scalaz is a bit of a mystery to me! EDIT: I guess what I'm asking here is not "how do I write this?" but "What is the correct name and signature for such a function and does it have anything to do with FP stuff I do not yet understand like Kleisli, Comonad etc?"

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• How to combine Option values in Scala?

  - by Jeff

  Hi! I want to be able to apply an operation f: (T,T) => T to two Option[T] values in Scala. I want the result to be None if any of the two values is None. More specifically, I want to know if is there a shorter way to do the following: def opt_apply[T](f: (T,T) => T, x: Option[T], y: Option[T]): Option[T] = { (x,y) match { case (Some(u),Some(v)) => Some(f(u,v)) case _ => None } } I have tryied (x zip y) map {case (u,v) => f(u,v)} but the result is an Iterator[T] not an Option[T]. Any help will be appreciated. Thanks.

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• The return value should be a list but doesn't return as expected?! - Python newbie

  - by user1432941

  Hi this must be a very simple solution that has eluded me this last hour. I've tried to build this test function where the return value of the test_cases list should match the values in the test_case_answers list but for some reason, test case 1 and test case 2 fail. When i print the return values for the test cases they return the correct answers, but for some reason test case 1 and test case 2 return False. Thanks for your help! import math test_cases = [1, 9, -3] test_case_answers = [1, 3, 0] def custom_sqrt(num): for i in range(len(test_cases)): if test_cases[i] >= 0: return math.sqrt(test_cases[i]) else: return 0 for i in range(len(test_cases)): if custom_sqrt(test_cases[i]) != test_case_answers[i]: print "Test Case #", i, "failed!" custom_sqrt(test_cases)

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• Simple Sinatra Ajax Not Working

  - by proteantech

  I was trying make an AJAX call from a static file on my computer to a simple sinatra service. The ajax call was returning with an error and no details. The server logged no errors either. Another strange symptom was that the Origin in the request header was null. I turns out that you can't make cross domain ajax calls without a little extra effort. You can set the Access-Control-Allow-Origin header on your sinatra response to expose your service to external domains using a snippet like this: get '/hi' do response['Access-Control-Allow-Origin'] = '*' content_type 'text/plain' "Hello World" end There's also another header you can set to allow other HTTP Methods besides gets, Access-Control-Request-Method. You can find more information by searching around for CORS: Cross Origin Resource Sharing and the previously mentioned headers. Oh, and in case you want to do this in Rails as well you can do something like this in your controller: after_filter :set_access_control_headers def set_access_control_headers headers['Access-Control-Allow-Origin'] = '*' headers['Access-Control-Request-Method'] = '*' end

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• Methods specific only to an instance? What are they called in Ruby?

  - by daremarkovic

  I know there are "instance methods", "class methods" but what are these types of methods called, for eg: s1 = "This is my STRING!" def s1.m1 downcase end p s1 # => "This is my STRING!" p s1.m1 # => "this is my string!" What type of method is the "m1" method called on the s1 "instance" of the "string" class? It's really weird because I didn't know this was possible at all if I try: s2 = "This is ANOTHER string" s2.m1 # => Won't work! Which kind of makes sense, but not sure why defining methods like m1 on instances on a class are useful at all.

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• Python: How to use code.InteractiveConsole?

  - by Rosarch

  I'm trying to use InteractiveConsole to create a new front-end for a Python interpreter. These code fragments are from me playing around with InteractiveConsole in IDLE: >>> ses = code.InteractiveConsole() >>> ses.runsource("def foo():") True >>> ses.runsource(" return 2") File "<input>", line 1 SyntaxError: 'return' outside function (<input>, line 1) False Why does it raise a syntax error? How else can I finish writing the function? Also, for something like this: >>> ses.runsource("x = 1") False >>> ses.runsource("x") 1 False How can I capture the 1 value from above? False is the return value, but 1 is written to some stream.

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• python compare time

  - by Jesse Siu

  i want to using python create filter for a log file. get recent 7 days record. but when i didn't know how to compare time. like current time is 11/9/2012, i want to get records from 04/9/2012 to now the log file like Sat Sep 2 03:32:13 2012 [pid 12461] CONNECT: Client "66.249.68.236" Sat Sep 2 03:32:13 2012 [pid 12460] [ftp] OK LOGIN: Client "66.249.68.236", anon password "[email protected]" Sat Sep 2 03:32:14 2012 [pid 12462] [ftp] OK DOWNLOAD: Client "66.249.68.236", "/pub/10.5524/100001_101000/100022/readme.txt", 451 i using this one def OnlyRecent(line): print time.strptime(line.split("[")[0].strip(),"%a %b %d %H:%M:%S %Y") print time.time() if time.strptime(line.split("[")[0].strip(),"%a %b %d %H:%M:%S %Y") < time.time(): return True return False But it shows (2012, 9, 2, 3, 32, 13, 5, 246, -1) 1347332968.08 (2012, 9, 2, 3, 32, 13, 5, 246, -1) 1347332968.08 (2012, 9, 2, 3, 32, 14, 5, 246, -1) 1347332968.08 the time format is different, and it can't compare time. So how to set this comparison in 7 days. Thanks

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• KindError: Property r must be an instance of SecondModel, why ?

  - by zjm1126

  class FirstModel(db.Model): p = db.StringProperty() r=db.ReferenceProperty(SecondModel) class SecondModel(db.Model): r = db.ReferenceProperty(FirstModel) class sss(webapp.RequestHandler): def get(self): a=FirstModel() a.p='sss' a.put() b=SecondModel() b.r=a b.put() a.r=b a.put() self.response.out.write(str(b.r.p)) the error is : Traceback (most recent call last): File "D:\Program Files\Google\google_appengine\google\appengine\ext\webapp\__init__.py", line 511, in __call__ handler.get(*groups) File "D:\zjm_code\helloworld\a.py", line 158, in get a.r=b File "D:\Program Files\Google\google_appengine\google\appengine\ext\db\__init__.py", line 3009, in __set__ value = self.validate(value) File "D:\Program Files\Google\google_appengine\google\appengine\ext\db\__init__.py", line 3048, in validate (self.name, self.reference_class.kind())) KindError: Property r must be an instance of SecondModel thanks

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• Delayed evaluation in Clojure

  - by StackedCrooked

  I'm having some trouble understanding how the delay macro works in Clojure. It doesn't seem to do what expect it to do (that is: delaying evaluation). As you can see in this code sample: ; returns the current time (defn get-timestamp [] (.getTime (java.util.Date.))) ; var should contain the current timestamp after calling "force" (def current-time (delay (get-timestamp))) However, calling current-time in the REPL appears to immediately evaluate the expression, even without having used the force macro: user=> current-time #<Delay@19b5217: 1276376485859> user=> (force current-time) 1276376485859 Why was the evaluation of get-timestamp not delayed until the first force call?

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