December 2005 - Zope

sessions in the presence of conflicts
by Dennis Allison 15 Dec '05

15 Dec '05

Zope 2.8.4, ZODB 3.4.2 I am still trying to resolve a "session variables in the presence of conflicts" problem. The observed symptom is that suddenly either some session variables disappear or all session variables disappear. In both cases, Zope has raised a KeyError exception for the a particular session variable because it is not present and an attempt was being made to access it from the session. The cause appears to be related to the presence of a conflict error and a botched recovery, but the exact mechanism remains a mystery. Zope equates a session object with a TransientObject. For our instance, that's fine, since our only TransientObject is a session. For the general case, I would have thought a SessionObject inheriting from TransiendObject would have been used so that conflict resolution for sessions could be easily specialized. The conflict resolution for a TransientObject (that is, a Session Object) is clearly suboptimal. In the next paragraphs I'll review what is currently done and then propose a different approach which I am about to implement for our systems. Comments, corrections, and suggestions much appreciated. _p_resolveConflict(self, oldState, savedState, newState) returns the state of the object after resolving different changes. The arguments are: oldState -- state of the object at the beginning of the current transaction (mutable) savedState -- state currently stored in the database. This state was written after oldState and reflect changes made by a transaction that committed before the current transaction (immutable) newState -- state after changes made by the current transaction (immutable) The standard conflict resolution for a TransientObject resolves according to the following rules: 1. if any of the states are invalid (that is, has a key '_invalid') return the invalid state. 2. if any any of the attributes ['token','id','_created'] differ then there is a conflict, raise the conflict exception. 3. choose the state most recently modified, if possible. 4. otherwise, choose the state most recently accessed. It seems to me that we can do much better for sessions because we know a bit about the semantics of sessions. A session object is a dictionary-like object mapping key-value pairs. Adding or deleting keys or changing the value associated with a key are independent operations and do not conflict unless the keys are duplicated in both the transactions. Any conflict resolution mechanism needs to be able to manage multiple keys independently since the session object is modified as a unit. In addition, new keys may be added and old keys deleted; any conflict resolution mechanism at the key level needs to be comprehend those operations. A more session-friendly conflict resolution might use: 1. if any of the states are invalid (that is, has a key '_invalid') return the invalid state. 2. if any any of the states attributes ['token','id','_created'] differ then there is a conflict, raise the conflict exception. 3. order the newState and savedState by modification time (or if that cannot be computed, by access time). 4. any key appearing in oldState's dictionary but not appearing in both savedState and newState should be removed from all. This corresponds to a key-value pair being deleted in one of the transactions. Insertions will be managed automatically by the updates. 5. beginning with the oldest, update oldState dictionary of key-value pairs using the dictionary part of newState and savedState. Return oldState. This does several things. First, it captures independent key-value changes made in both potentially conflicting transactions. Second, it provides a reasonable ordering for multiple (potentially conflicting) key-value pair updates. Third, it manages insertions and deletions to the session variable set in the presence of conflicts. Does this make sense? I have yet to figure out how to map a TransientObject "state" back to the object it represents, but it clearly is possible.

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HTTP compressed response
by Gabriel Genellina 15 Dec '05

15 Dec '05

Hello I wish to enable HTTP response compression. Looking at ZPublisher\HTTPResponse.py I see this method: def enableHTTPCompression(self,REQUEST={},force=0,disable=0,query=0): and I think I should invoke it with REQUEST=REQUEST to enable compression only when the client browser can handle it. But I dont know WHEN to do the call - should it be in (every) template used to generate a response? should I modify the response factory (make_response in ZServer\HTTPResponse.py) to invoke this? or what? Gabriel Genellina Softlab SRL

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Unauthorized exception when trying to access a list item
by Cameron Beattie 15 Dec '05

15 Dec '05

I am trying to access a value in a list. The script getDIDS_list is passed a list called listoflists: list = listoflists ret = [] tup = (0,1,2) factortup = (1,2) factor = 2 for i in range(len(list)): # 1 == 1 if i in tup: if i in factortup: x = list[i] * factor etc The code is a bit strange due to my testing. However zope gets upset when trying to evaluate list[i]: You are not allowed to access '1' in this context a.. Module Products.PageTemplates.ZRPythonExpr, line 47, in __call__ __traceback_info__: context.getDIDS_list(listoflists = DIDs) a.. Module Python expression "context.getDIDS_list(listoflists = DIDs)", line 1, in <expression> a.. Module Shared.DC.Scripts.Bindings, line 311, in __call__ a.. Module Shared.DC.Scripts.Bindings, line 348, in _bindAndExec a.. Module Products.PythonScripts.PythonScript, line 323, in _exec a.. Module None, line 10, in getDIDS_list <PythonScript at /Conversant/account/getDIDS_list> Line 10 a.. Module AccessControl.ZopeGuards, line 71, in guarded_getitem a.. Module AccessControl.ImplPython, line 529, in validate a.. Module AccessControl.ImplPython, line 329, in validate I've tried calling the script from the page template using here.getDIDS_list, container.getDIDS_list context.getDIDS_list but the problem persists. Am I accessing the list in the wrong way? Any advice would be appreciated. Regards Cameron

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XML-RPC within ZOPE
by Jan-Ole Esleben 15 Dec '05

15 Dec '05

Hi! Is it at all impossible to use XML-RPC _within_ a ZOPE architecture? What I mean is: I have a nested call structure: 1. Python script calls a method from a ZODB object 2. That method calls a Python module function 3. That module function dispatches an XML-RPC call to the same ZODB object called in step 1 4. This last call, which is rather complex, returns, and all the calls leading up to it return, sometimes doing some minor work When I use the same code _without_ any XML-RPC (the Zope server's self instead of the XML-RPC server object for that server), it works just fine. When I use XML-RPC, I get a ConflictError during the final return (from step 1), and I get it if I commit manually beforehand, so it must be the commit triggering it. The tricky thing is: nothing in my ZODB changes. I have several mutable _arguments_ that are passed on, but they are not default arguments and they don't get written to the ZODB. Is what I'm trying to do impossible for some reason? Or can I just make the whole call take place outside any transactions? Thanks in advance for any pointers, I'm really a little desparate at this point. Ole

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Plone not installing on Zope
by Qass 15 Dec '05

15 Dec '05

Hi: I installed Zope 2.8.4 and moved all folders from the untarred Plone 2.1.1 download to the Products folder of the instance of Zope I'm running in my home directory. I have Python 2.3.5. However, as the Plone installation instructions mention, "Plone Site" does not show up in the drop down menu of items in the ZMI. I've tried different versions of Plone to no avail. What am I doing wrong here? Thanks Qass

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dynamic js lists
by raharley＠mailshack.com 15 Dec '05

15 Dec '05

Hi all Following up on my other post and having a read on quirksmode (thanks Peter). I came up with the following which unsuprising doesnt want to work. Could anyone point out any blindingly obvious code errors? I think it could perhaps be something to do with the cells number, ie cell[0] etc. Thanks Rich <html> <head> <title>Untitled Document</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <meta http-equiv="Content-Style-Type" content="text/css"> <meta http-equiv="Content-Script-Type" content="text/javascript"> <script type="text/javascript"> var rows; onload = function(){ var heavyArr=[]; var softArr=[]; var goodtosoftArr=[]; goodArr=[]; var goodtofirmArr=[]; var firmArr=[]; rows = document.getElementById('mytab').getElementsByTagName('tr'); for (var i=1;i<rows.length;i++){ var cells = rows[i].getElementsByTagName('td'); heavyArr[heavyArr.length]=[Number(cells[0].firstChild.data),'h']; softArr[softArr.length]=[Number(cells[1].firstChild.data),'s']; goodtosoftArr[goodtosoftArr.length]=[Number(cells[2].firstChild.data),'gts'] ; goodArr[goodArr.length]=[Number(cells[3].firstChild.data),'g']; goodtofirmArr[goodtofirmArr.length]=[Number(cells[4].firstChild.data),'gtf'] ; firmArr[firmArr.length]=[Number(cells[5].firstChild.data),'f']; } arrMax=['','',sortA(heavyArr),sortA(softArr),sortA(goodtosoftArr)],sortA(goo dArr)], sortA(goodtofirmArr)], sortA(firmArr)]; } function sortA(a){ var b= a.sort(function (a, b) {return a[0] == b[0] ? 0 : (a[0] < b[0] ? -1 : 1)}); return b[b.length-1][0]; } function highl(q){ for(var i=1;i<rows.length;i++){ var val = Number(rows[i].getElementsByTagName('td')[q].firstChild.data); rows[i].style.backgroundColor=(val==arrMax[q])?'#66ccff':''; } } </script> </head> <body> <select id="sel" onchange="highl(this.selectedIndex+1)"> <option> -- select --</option> <option value="heavy rating">heavy rating</option> <option value="soft rating">soft rating</option> <option value="goodtosoft rating">goodtosoft rating</option> <option value="good rating">good rating</option> <option value="goodtofirm rating">goodtofirm rating</option> <option value="firm rating">firm rating</option> </select> <br> <br> TABLE GOES HERE WITH ID=mytab </html> -------------------------------------------------------------------- mail2web - Check your email from the web at http://mail2web.com/ .

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Re: [Zope] Trapping zope exceptions in python script
by Tino Wildenhain 15 Dec '05

15 Dec '05

... > > Try: > > context.afolder.manage_delObjects(['someitem']) > > where 'someitem' does not exist in 'afolder' works: try: context.afolder.manage_adlObjects(['nonexistent']) except Exception,x: if 'BadRequest' in repr(x): print "bad request" else: raise x :-) (Ok, this _is_ ugly, but at least works. Certainly these exception types should be importable or even immediately available for python scripts)

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RE: [Zope] Zope 2.8.4+Latest cygwin installation
by Pascal Peregrina 15 Dec '05

15 Dec '05

Ok, just found it has already been reported several months ago, even with python 2.3.x: http://www.zope.org/Collectors/Zope/1725 Does someone know of any kind of temporary workaround for this ? Thanks ! Pascal -----Message d'origine----- De : zope-bounces(a)zope.org [mailto:zope-bounces@zope.org] De la part de Pascal Peregrina Envoyé : jeudi 15 décembre 2005 12:25 À : zope(a)zope.org Objet : [Zope] Zope 2.8.4+Latest cygwin installation Hi, I would like to know if anyone has been able to compile and run Zope 2.8.4 with Cygwin. I just installed cygwin with latest stable packages. I compiled python 2.4.2 (I know, not the supported version, so I am about to try 2.3.5 now) I had issues with the socket module, and from google I applied a workaround that worked fine : in Modules/socketmodule.c Change : #if defined(__sgi) && !defined(INET_ADDRSTRLEN) #define INET_ADDRSTRLEN 16 #endif To : /*#if defined(__sgi) && !defined(INET_ADDRSTRLEN)*/ #define INET_ADDRSTRLEN 16 /*#endif*/ I made several python tests and all looks fine. Then I compiled Zope 2.8.4 without any issue. But when I run it, I get this error: Site Error An error was encountered while publishing this resource. exceptions.TypeError Sorry, a site error occurred. Traceback (innermost last): Module ZPublisher.Publish, line 187, in publish_module_standard Module Products.Localizer, line 58, in new_publish Module ZPublisher.Publish, line 144, in publish Module Zope2.App.startup, line 174, in zpublisher_exception_hook Module App.ZApplication, line 60, in __bobo_traverse__ Module UserDict, line 17, in __getitem__ Module ZODB.Connection, line 704, in setstate Module ZODB.Connection, line 760, in _setstate Module ZODB.serialize, line 495, in setGhostState Module ZODB.serialize, line 488, in getState Module ZODB.serialize, line 436, in _persistent_load Module ZODB.Connection, line 208, in get Module ZODB.serialize, line 482, in getGhost TypeError: Acquirer.__new__(Application) is not safe, use Persistence.Persistent.__new__() Does anyone know what I can do ? Thanks a lot. Pascal ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com ********************************************************************** _______________________________________________ Zope maillist - Zope(a)zope.org http://mail.zope.org/mailman/listinfo/zope ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope-dev )

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Zope 2.8.4+Latest cygwin installation
by Pascal Peregrina 15 Dec '05

15 Dec '05

Hi, I would like to know if anyone has been able to compile and run Zope 2.8.4 with Cygwin. I just installed cygwin with latest stable packages. I compiled python 2.4.2 (I know, not the supported version, so I am about to try 2.3.5 now) I had issues with the socket module, and from google I applied a workaround that worked fine : in Modules/socketmodule.c Change : #if defined(__sgi) && !defined(INET_ADDRSTRLEN) #define INET_ADDRSTRLEN 16 #endif To : /*#if defined(__sgi) && !defined(INET_ADDRSTRLEN)*/ #define INET_ADDRSTRLEN 16 /*#endif*/ I made several python tests and all looks fine. Then I compiled Zope 2.8.4 without any issue. But when I run it, I get this error: Site Error An error was encountered while publishing this resource. exceptions.TypeError Sorry, a site error occurred. Traceback (innermost last): Module ZPublisher.Publish, line 187, in publish_module_standard Module Products.Localizer, line 58, in new_publish Module ZPublisher.Publish, line 144, in publish Module Zope2.App.startup, line 174, in zpublisher_exception_hook Module App.ZApplication, line 60, in __bobo_traverse__ Module UserDict, line 17, in __getitem__ Module ZODB.Connection, line 704, in setstate Module ZODB.Connection, line 760, in _setstate Module ZODB.serialize, line 495, in setGhostState Module ZODB.serialize, line 488, in getState Module ZODB.serialize, line 436, in _persistent_load Module ZODB.Connection, line 208, in get Module ZODB.serialize, line 482, in getGhost TypeError: Acquirer.__new__(Application) is not safe, use Persistence.Persistent.__new__() Does anyone know what I can do ? Thanks a lot. Pascal ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com **********************************************************************

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Stepper 1.4.1 Released!
by Chris Withers 15 Dec '05

15 Dec '05

Stepper is a framework for performing asynchronous tasks on Zope servers. This is a bug fix release that corrects some problems with the 1.4.0 release. The major bugs fixed for this release were: - Write conflict errors are now handled in the same way as read conflict errors. - Stepper is no longer left locked if a conflict error occurs. - Nothing is now logged to the console in quiet mode, even with Zope 2.8. Several other small bugs were also fixed. For more information, please see: http://www.simplistix.co.uk/software/zope/stepper cheers, Chris -- Simplistix - Content Management, Zope & Python Consulting - http://www.simplistix.co.uk

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