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  • List of Django model instance foreign keys losing consistency during state changes.

    - by Joshua
    I have model, Match, with two foreign keys: class Match(model.Model): winner = models.ForeignKey(Player) loser = models.ForeignKey(Player) When I loop over Match I find that each model instance uses a unique object for the foreign key. This ends up biting me because it introduces inconsistency, here is an example: >>> def print_elo(match_list): ... for match in match_list: ... print match.winner.id, match.winner.elo ... print match.loser.id, match.loser.elo ... >>> print_elo(teacher_match_list) 4 1192.0000000000 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 >>> teacher_match_list[0].winner.elo = 3000 >>> print_elo(teacher_match_list) 4 3000 # Object 4 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 # Object 4 >>> I solved this problem like so: def unify_refrences(match_list): """Makes each unique refrence to a model instance non-unique. In cases where multiple model instances are being used django creates a new object for each model instance, even if it that means creating the same instance twice. If one of these objects has its state changed any other object refrencing the same model instance will not be updated. This method ensure that state changes are seen. It makes sure that variables which hold objects pointing to the same model all hold the same object. Visually this means that a list of [var1, var2] whose internals look like so: var1 --> object1 --> model1 var2 --> object2 --> model1 Will result in the internals being changed so that: var1 --> object1 --> model1 var2 ------^ """ match_dict = {} for match in match_list: try: match.winner = match_dict[match.winner.id] except KeyError: match_dict[match.winner.id] = match.winner try: match.loser = match_dict[match.loser.id] except KeyError: match_dict[match.loser.id] = match.loser My question: Is there a way to solve the problem more elegantly through the use of QuerySets without needing to call save at any point? If not, I'd like to make the solution more generic: how can you get a list of the foreign keys on a model instance or do you have a better generic solution to my problem? Please correct me if you think I don't understand why this is happening.

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  • How long do FireFox, Chrome, Safari, and Opera cache SSL/TLS session keys?

    - by MJ
    To try to use a reason SSL/TLS session key timeout on the server-side, I'd like to know how long popular browsers cache session keys on the client. Microsoft describes this information for Windows/IE here: http://technet.microsoft.com/en-us/library/cc776467(WS.10).aspx But, I haven't been able to find similar information for other popular browsers. Does anyone know? Thanks!

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  • Berkeley DB: btree prefix comparison for directory-like keys?

    - by Mark Harrison
    I'm going to index a BDB with keys that look a lot like directory paths ('/foo/bar', '/foo/baz', etc, with levels of slashes generally < 10). Does anybody have any experience with using a Btree prefix comparison routine[1] for this? Are the savings worthwhile? Any references to experience papers on this subject? [1] http://www.stanford.edu/class/cs276a/projects/docs/berkeleydb/ref/am_conf/bt_prefix.html

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  • Swing's KeyListener and multiple keys pressed at the same time.

    - by Negai
    Hi everyone, is there any conventional way in swing of tracking down the events, when two keyboard keys are pressed at the same time? I have a couple of ideas e.g. remembering the key and event generation time so that we could in a consecutive event handler invocation check the time difference between these two events and decide, whether it's a two-button event or not. Phew. But it looks like a kludge. Thanks in advance.

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  • Are GUID primary keys bad in theory, or just practice?

    - by Yarin
    Whenever I design a database I automatically start with an auto-generating GUID primary key for each of my tables (excepting look-up tables) I know I'll never lose sleep over duplicate keys, merging tables, etc. To me it just makes sense philosophically that any given record should be unique across all domains, and that that uniqueness should be represented in a consistent way from table to table. I realize it will never be the most performant option, but putting performance aside, I'd like to know if there are philosophical arguments against this practice?

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  • how to create a system-wide independent universal counter object primarily for Database keys?

    - by andora
    I would like to create/use a system-wide independent universal 'counter object' that can be called via COM in a thread-safe manner. The counter object will be passed an ID to identify which counter to return, handle the counting, 'persist' the count (occasionally), have reasonable performance (as fast as possible) perhaps capable of 1000 counts per second or better (1mS) and be accessible cross-process/out-of-process. The current count status must be persisted between object restarts/shutdowns. The counter object is liklely to be a 'singleton' type object implemented in some form of free-threaded dictionary, containing maybe 10 counters (perhaps 50 max). The count needs to be monotonic and consistent, (ie: guaranteed unique sequential values). Each counter should have a few methods, like reset, inc, dec, set, clear, remove. As a luxury, I would like to have a variable-increment (ie: 'step by' value). To support thread-safefty, perhaps some sorm of critical-section or mutex call. It just needs to return a long/4byte signed integer. I really want something that can be called from anywhere, including VBScript, so I figure COM is my preferred solution. The primary use of this is for database keys. I am unable to use autoinc or guid type keys and have ruled out database-generated counting systems at this point. I've spent days researching this and I have really struggled to find a solution. The best I can find is a free-threaded dictionary object that can be instantiated using COM+ from Motobit - it seems to offer all the 'basics' and I guess I could create some form of wrapper for this. So, here are my questions: Does such a 'general purpose counter-object already exist? Can you direct me to it? (MS did do an IIS/ASP object called 'MSWC.Counter' but this isn't 'cross-process'/ out-of-process component and isn't thread-safe. (but if it was, it would do!) What is the best way of creating such a Component? (I'd prefer VB6 right-now, [don't ask!] but can do in VB.NET2005 if I had to). I don't have the skills/knowledge/tools to use anything else. I am desparate for a workable solution. I need specific guidance! If anybody can code something up for me I am prepared to pay for it.

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  • Performance of String literals vs constants for Session[...] dictionary keys

    - by FreshCode
    Session[Constant] vs Session["String Literal"] Performance I'm retrieving user-specific data like ViewData["CartItems"] = Session["CartItems"]; with a string literal for keys on every request. Should I be using constants for this? If yes, how should I go about implementing frequently used string literals and will it significantly affect performance on a high-traffic site? Related question does not address ASP.NET MVC or Session.

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  • What do I need to distribute (keys, certs) for Python w/ SSL-socket connection?

    - by fandingo
    I'm trying to write a generic server-client application that will be able to exchange data amongst servers. I've read over quite a few OpenSSL documents, and I have successfully setup my own CA and created a cert (and private key) for testing purposes. I'm stuck with Python 2.3, so I can't use the standard "ssl" library. Instead, I'm stuck with PyOpenSSL, which doesn't seem bad, but there aren't many documents out there about it. My question isn't really about getting it working. I'm more confused about the certificates and where they need to go. Here are my two programs that do work: Server: #!/bin/env python from OpenSSL import SSL import socket import pickle def verify_cb(conn, cert, errnum, depth, ok): print('Got cert: %s' % cert.get_subject()) return ok ctx = SSL.Context(SSL.TLSv1_METHOD) ctx.set_verify(SSL.VERIFY_PEER|SSL.VERIFY_FAIL_IF_NO_PEER_CERT, verify_cb) # ?????? ctx.use_privatekey_file('./Dmgr-key.pem') ctx.use_certificate_file('Dmgr-cert.pem') # ?????? ctx.load_verify_locations('./CAcert.pem') server = SSL.Connection(ctx, socket.socket(socket.AF_INET, socket.SOCK_STREAM)) server.bind(('', 50000)) server.listen(3) a, b = server.accept() c = a.recv(1024) print(c) Client: from OpenSSL import SSL import socket import pickle def verify_cb(conn, cert, errnum, depth, ok): print('Got cert: %s' % cert.get_subject()) return ok ctx = SSL.Context(SSL.TLSv1_METHOD) ctx.set_verify(SSL.VERIFY_PEER, verify_cb) # ?????????? ctx.use_privatekey_file('/home/justin/code/work/CA/private/Dmgr-key.pem') ctx.use_certificate_file('/home/justin/code/work/CA/Dmgr-cert.pem') # ????????? ctx.load_verify_locations('/home/justin/code/work/CA/CAcert.pem') sock = SSL.Connection(ctx, socket.socket(socket.AF_INET, socket.SOCK_STREAM)) sock.connect(('10.0.0.3', 50000)) a = Tester(2, 2) b = pickle.dumps(a) sock.send("Hello, world") sock.flush() sock.send(b) sock.shutdown() sock.close() I found this information from ftp://ftp.pbone.net/mirror/ftp.pld-linux.org/dists/2.0/PLD/i586/PLD/RPMS/python-pyOpenSSL-examples-0.6-2.i586.rpm which contains some example scripts. As you might gather, I don't fully understand the sections between the " # ????????." I don't get why the certificate and private key are needed on both the client and server. I'm not sure where each should go, but shouldn't I only need to distribute one part of the key (probably the public part)? It undermines the purpose of having asymmetric keys if you still need both on each server, right? I tried alternating removing either the pkey or cert on either box, and I get the following error no matter which I remove: OpenSSL.SSL.Error: [('SSL routines', 'SSL3_READ_BYTES', 'sslv3 alert handshake failure'), ('SSL routines', 'SSL3_WRITE_BYTES', 'ssl handshake failure')] Could someone explain if this is the expected behavior for SSL. Do I really need to distribute the private key and public cert to all my clients? I'm trying to avoid any huge security problems, and leaking private keys would tend to be a big one... Thanks for the help!

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  • How do you check the presence of many keys in a Python dictinary?

    - by Thierry Lam
    I have the following dictionary: sites = { 'stackoverflow': 1, 'superuser': 2, 'meta': 3, 'serverfault': 4, 'mathoverflow': 5 } To check if there are more than one key available in the above dictionary, I will do something like: 'stackoverflow' in sites and 'serverfault' in sites The above is maintainable with only 2 key lookups. Is there a better way to handle checking a large number of keys in a very big dictionary?

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  • Clojure: I have many sorted maps and want to reduce in order all there values a super maps of keys -> vector

    - by Alex Foreman
    I have seen this but can't work out how to apply it (no pun intended) to my situation. I have a sorted list of maps like this: (note there can be more than two keys in the map) ({name1 3, name2 7}, {name1 35, name2 7}, {name1 0, name2 3}) What I am after is this data structure afterwards: ({:name1 [3,35,0]}, {:name2 [7,7,3]}) Ive been struggling with this for a while and cant seem to get anywhere near. Caveats: The data must stay sorted and I have N keywords not just two.

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  • Network bandwidth bottleneck for sorting of mapreduce intermediate keys?

    - by Zubair
    I have been learning the mapreduce algorithm and how it can potentially scale to millions of machines, but I don't understand how the sorting of the intermediate keys after the map phase can scale, as there will be: 1,000,000 x 1,000,000 : potential machines communicating small key / value pairs of the intermediate results with each other? Isn't this a bottleneck?

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  • Connect trough remote computer connection

    - by Didac
    First, sorry for my english and my poor knowlodge of this subject. I have a dedicated server placed in Germany (windows 2008 R2) and I live in spain. I would like to access internet from my home computer (Windows 7 Pro x64), trough my server in Germany, so I can use a German IP, what I need some times. I have complete acces in to both computers, but I just don't know where to start. (My knwoledge is limited to software development :/ ) I'd like to know where to start, if I need to create a VPN and so.. Thanks in advance! Update 1 I tried a lot of options of OpenVPN, but I sadly I know nothing abuot networking, so I have to accept I do not know what I'm doing :( Here are my config files (note most of the options are from the sample config files). server.conf #server config file start port 1194 proto udp dev tun server 10.0.0.0 255.255.255.224 #you may choose any subnet. 10.0.0.x is used for this example. ca "C:\\Program Files (x86)\\OpenVPN\\easy-rsa\\keys\\ca.crt" cert "C:\\Program Files (x86)\\OpenVPN\\easy-rsa\\keys\\server.crt" key "C:\\Program Files (x86)\\OpenVPN\\easy-rsa\\keys\\server.key" dh "C:\\Program Files (x86)\\OpenVPN\\easy-rsa\\keys\\dh1024.pem" push "redirect-gateway def1" push "dhcp-option DNS 8.8.8.8" #the following commands are optional keepalive 10 120 comp-lzo persist-key persist-tun verb 5 #config file ends client.conf #client config file start client dev tun proto udp remote 176.9.99.180 1194 resolv-retry infinite nobind persist-key persist-tun ca "C:\\Program Files (x86)\\OpenVPN\\easy-rsa\\keys\\ca.crt" cert "C:\\Program Files (x86)\\OpenVPN\\easy-rsa\\keys\\client1.crt" key "C:\\Program Files (x86)\\OpenVPN\\easy-rsa\\keys\\client1.key" ns-cert-type server comp-lzo verb 5 explicit-exit-notify 2 ping 10 ping-restart 60 route-method exe route-delay 2 # end of client config file And here's the server's network settings: IP address: 176.9.99.180 Subnet mask: 255.255.255.224 Default gateway: 176.9.99.161 Preferred DNS server: 127.0.0.1

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  • Solving the EXC_BAD_ACCESS in WhatATool Part 2

    - by Allen
    #import <Cocoa/Cocoa.h> @interface PolygonShape : NSObject { int numberOfSides, maximumNumberOfSides, minimumNumberOfSides; } @property (readwrite) int numberOfSides, maximumNumberOfSides, minimumNumberOfSides; @property (readonly) float angleInDegrees, angleInRadians; @property (readonly) NSString * name; @property (readonly) NSString * description; -(id) init; -(void) setNumberOfSides:(int)sides; -(void) setMinimumNumberOfSides:(int)min; -(void) setMaximumNumberOfSides:(int)max; -(float) angleInDegrees; -(float) angleInRadians; -(NSString *) name; -(id) initWithNumberOfSides:(int) sides minimumNumberOfSides:(int) min maximumNumberOfSides:(int) max; -(NSString *) description; -(void) dealloc; @end #import "PolygonShape.h" @implementation PolygonShape -(id) init { return [self initWithNumberOfSides:4 minimumNumberOfSides:3 maximumNumberOfSides:5]; } @synthesize numberOfSides, minimumNumberOfSides, maximumNumberOfSides, angleInRadians; -(void) setNumberOfSides:(int)sides { numberOfSides = sides; NSLog(@"The number of sides is off limit so the number of sides is %@.",sides); } -(void)setMaximumNumberOfSides:(int)max { if (maximumNumberOfSides <= 12) { maximumNumberOfSides = max; } } -(void)setMinimumNumberOfSides: (int)min { if (minimumNumberOfSides > 2) { minimumNumberOfSides = min; } } - (id)initWithNumberOfSides:(int)sides minimumNumberOfSides:(int)min maximumNumberOfSides:(int)max { if(self=[super init]) { [self setNumberOfSides:(int)sides]; [self setMaximumNumberOfSides:(int)max]; [self setMinimumNumberOfSides: (int)min]; } return self; } -(float) angleInDegrees { float anglesInDegrees = (180 * (numberOfSides - 2) / numberOfSides); return anglesInDegrees; } -(float)angleInRadiants { float anglesInRadiants = ((180 * (numberOfSides - 2) / numberOfSides) * (180 / M_PI)); return anglesInRadiants; } -(NSString *)name { NSString * output; switch (numberOfSides) { case 3: output = @"Triangle"; break; case 4: output = @"Square"; break; case 5: output = @"Pentagon"; break; case 6: output = @"Hexagon"; break; case 7: output = @"Heptagon"; break; case 8: output = @"Octagon"; break; case 9: output = @"Nonagon"; break; case 10: output = @"Decagon"; break; case 11: output = @"Hendecagon"; break; case 12: output = @"Dodecabgon"; break; default: output = @"Invalid number of sides: %i is greater than maximum of five allowed."; } return output; } -(NSString *)description { NSString * output; NSLog(@"Hello I am a %i-sided polygon (aka a %@) with angles of %f degrees (%f radians).", numberOfSides, output, [self angleInDegrees], [self angleInRadiants]); return [self description]; } -(void)dealloc { [super dealloc]; } @end #import <Foundation/Foundation.h> #import "PolygonShape.h" void PrintPathInfo() { NSLog(@"Section 1"); NSLog(@"--------------------"); NSString *path = [@"~" stringByExpandingTildeInPath]; NSLog(@"My home folder is at '%@'.", path); NSArray *pathComponent = [path pathComponents]; for (path in pathComponent) { NSLog(@"%@",path); } NSLog(@"--------------------"); NSLog(@"\n"); } void PrintProcessInfo() { NSLog(@"Section 2"); NSLog(@"--------------------"); NSString * processName = [[NSProcessInfo processInfo] processName]; int processIdentifier = [[NSProcessInfo processInfo] processIdentifier]; NSLog(@"Process Name: '%@', Process ID: '%i'", processName, processIdentifier); NSLog(@"--------------------"); NSLog(@"\n"); } void PrintBookmarkInfo() { NSLog(@"Section 3"); NSLog(@"--------------------"); NSArray * keys = [NSArray arrayWithObjects: @"Stanford University", @"Apple", @"CS193P", @"Stanford on iTunes U", @"Stanford Mall", nil]; NSArray * objects = [NSArray arrayWithObjects: [NSURL URLWithString: @"http://www.stanford.edu"], @"http://www.apple.com", @"http://cs193p.stanford.edu", @"http://itunes.stanford.edu", @"http://stanfordshop.com",nil]; NSMutableDictionary * dictionary = [NSMutableDictionary dictionaryWithObjects:objects forKeys:keys]; NSEnumerator * enumerator = [keys objectEnumerator]; for (id keys in dictionary) { NSLog(@"key: '%@', value: '%@'", keys, [dictionary objectForKey:keys]); } NSLog(@" "); NSLog(@"These are the ones that has the prefix 'Stanford'."); NSLog(@" "); id object; while (object = [enumerator nextObject]) { if ([object hasPrefix: @"Stanford"]) { NSLog(@"key: '%@', value: '%@'", object, [dictionary objectForKey:object]); } } NSLog(@"--------------------"); NSLog(@"\n"); } void PrintIntrospectionInfo() { NSLog(@"Section 4"); NSLog(@"--------------------"); SEL lowercase = @selector (lowercaseString); NSMutableArray * array = [NSMutableArray array]; [array addObject: [NSString stringWithString: @"Here is a string"]]; [array addObject: [NSDictionary dictionary]]; [array addObject: [NSURL URLWithString: @"http://www.stanford.edu"]]; [array addObject: [[NSProcessInfo processInfo]processName]]; for (id keys in array) { NSLog(@"\n"); NSLog(@"Class Name: %@", [keys className]); NSLog(@"Is Member of NSString: %@", [keys isMemberOfClass:[NSString class]]?@"Yes":@"No"); NSLog(@"Is Kind of NSString: %@", [keys isKindOfClass:[NSString class]]?@"Yes":@"No"); if ([keys respondsToSelector: lowercase]==YES) { NSLog(@"Responds to lowercaseString: %@",[keys respondsToSelector: lowercase]?@"Yes":@"No"); NSLog(@"lowercaseString is: %@", [keys performSelector: lowercase]); } else { NSLog(@"Responds to lowercaseString: %@",[keys respondsToSelector: lowercase]?@"Yes":@"No" ); } } NSLog(@"--------------------"); } void PrintPolygonInfo() { NSMutableArray * array = [NSMutableArray array]; PolygonShape * polygon1 = [[PolygonShape alloc]initWithNumberOfSides:4 minimumNumberOfSides:3 maximumNumberOfSides:7]; [array addObject:polygon1]; [array description]; PolygonShape * polygon2 = [[PolygonShape alloc]initWithNumberOfSides:6 minimumNumberOfSides:5 maximumNumberOfSides:9]; [array addObject:polygon2]; [array description]; PolygonShape * polygon3 = [[PolygonShape alloc]initWithNumberOfSides:12 minimumNumberOfSides:9 maximumNumberOfSides:12]; [array addObject:polygon3]; [array description]; [array release]; [polygon1 release]; [polygon2 release]; [polygon3 release]; } int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; PrintPathInfo(); PrintProcessInfo(); PrintBookmarkInfo(); PrintIntrospectionInfo(); PrintPolygonInfo(); [pool release]; return 0; } //The result was "EXC_BAD_ACCESS", but I couldn't figure out how to resolve this problem.

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  • Can one config LDAP to accept auth from ssh-agent instead of from Kerberos?

    - by Alex North-Keys
    [This question is not about getting your LDAP password to authenticate you for SSH logins. We have that working just fine, thank you :-) ] Let's suppose you're on a Linux network (Ubuntu 11.10, slapd 2.4.23), and you need to write a set of utilities that will use ldapmodify, ldapadd, ldapdelete, and so on. You don't have Kerberos, and don't want to deal with its timeouts (most users don't know how to get around this), quirks, etc. This resolves the question to one of where else to get credentials to feed to LDAP, probably through GSSAPI - which technically doesn't require Kerberos despite its dominance there - or something like it. However, nearly everyone seems to have an SSH agent program, complete with its key cache. I'd really like an ssh-add to be sufficient to allow passwordless LDAP command use. Does anyone know of a project working on using the SSH agent as the source of authentication to LDAP? It might be through an ssh-aware GSSAPI layer, or some other trick I haven't thought of. But it would be wonderful for making LDAP effortless. Assuming I haven't just utterly missed a way to use ldapmodify and kin without having to type my LDAP passwords - using -x is NOT acceptable. At my site, the LDAP server only accepts ldaps connections, and requires authentication for modifying operations. Those are requirements, of course. Any ideas would be greatly appreciated. :-)

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  • Can zlib.crc32 or zlib.adler32 be safely used to mask primary keys in URLs?

    - by David Eyk
    In Django Design Patterns, the author recommends using zlib.crc32 to mask primary keys in URLs. After some quick testing, I noticed that crc32 produces negative integers about half the time, which seems undesirable for use in a URL. zlib.adler32 does not appear to produce negatives, but is described as "weaker" than CRC. Is this method (either CRC or Adler-32) safe for usage in a URL as an alternate to a primary key? (i.e. is it collision-safe?) Is the "weaker" Adler-32 a satisfactory alternative for this task? How the heck do you reverse this?! That is, how do you determine the original primary key from the checksum?

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