March 2000 - Zope - Zope lists

RE: [Zope] Zope needs this (and Dynamo has it)
by Alexander Staubo 07 Mar '00

07 Mar '00

And here follows part two of my follow-up. (I'm all thumbs today -- why is Alt+S so damn accessible on a PC keyboard? ;-) > From: Thomas Stenhaug [mailto:thomas@src.no] > Sent: Sunday, March 05, 2000 2:34 PM > To: Alexander Staubo > Cc: Zope Mailing List (E-mail) > Subject: Re: [Zope] Zope needs this (and Dynamo has it) > > | This situation has nothing to do with open vs. closed, either. Just > | like Zope we're talking about proprietary (as opposed to standarized > | -- DTML may be open, but it's still proprietary) > > I don't quite grok what "the situation" is referring to, Read the preceding paragraph, about Java and the "cost of training a person in the arts of Zope". >but I think > you're wrong here, or at least mistaken regarding the meaning of > "proprietary". Proprietary, according to Merriam-Webster, means this: > > [cut from Merriam-Webster] > Function: adjective > Etymology: Late Latin proprietarius, from Latin proprietas property -- > more at PROPERTY > Date: 1589 > 1 : of, relating to, or characteristic of a proprietor > <proprietary rights> > 2 : used, made, or marketed by one having the exclusive legal right > <a proprietary process> > 3 : privately owned and managed and run as a profit-making > organization <a proprietary clinic> > [/] I mean proprietary as being controlled by a private party -- owned, in a very liberal sense -- as opposed to being standarized. XML is not proprietary. DTML and Java are. I'm not as knowledge about IP laws as I would like to be, so I can't really defend my use of this word or whether DTML is an intellectual property of Digital Creations. Perhaps somebody else more suited to the task could clarify. > [...] > | and Zope, despite its many powerful features, is not big enough for > | truly big things. > | > | This is a two-part problem. The first part is that Zope's bullshit > | factor is too low; > [...] > | We tech people know better, we know a shiny surface tells us nothing > | about the engine underneath, but we tech people are not holding the > | crucial component -- those big brown bags of money. > > I'm not sure if I agree it's a problem, then, that Zope lacks in the > big-department. :-) If the suits in managements (assuming you work in such a place) tell you to go learn Dynamo because that's what they want to use, wouldn't you say it's a problem? > | [under Zope's surface] lies a powerful engine with scalability > | problems. > > What part of Zope's engine are you referring to here? Do you mean > Python in general, are some specific part? Like ZODB? I definitely believe that Python is Zope's largest problem right now. It's also, from a technical point of view, one of it's biggest assets -- Zope is becoming the killer application of Python, and might eventually become the driving force to evolve Python, which is, I believe, suffering from draught into the contributor department. Skilled developers aren't flocking to Python to make it faster. Not right now, anyway. My hope is that Zope will change this, because Python has possibly one of the slowest interpreters on earth. Python zealots -- and there is such a beast -- will tell you that Python's performance is less of a matter because what you sacrifice in speed you gain in power, ie. computational expressiveness through a high-level, dynamic language. For an example of a good, Python-like, dynamic language that is also very fast, take a look at Dylan. In current implementations, Dylan is not interpreted but rather compiled to native code, but in theory there is nothing stopping anyone from writing a highly efficient Dylan interpreter. Dylan's magic comes from its use of type hints, a system which I had recognized as likely pivotal to improving Python's interpreter long before I knew of Dylan. In Dylan, specifying a variable's type is optional. When omitted, the Dylan compiler will usually be able to infer the type from what you do with the variable (ie., it sees you're assigning an integer to it; hence it can assume that, for at least a stretch of execution, the variable remains an integer). When you explicitly declare a variable's type, Dylan applies the necessary code optimizations (such as using tight integer maths or string copying) as well as static type checking. In Python, variables can hold virtually anything, and this incurs a huge amount of checks. Just imagine -- while Zope is running, thousands and thousands of the same little checks are performed continuously, over and over again, amounting to no uncertain overhead. Python's biggest overhead comes from its dynamism -- the dynamic typing, as explained, combined the object allocation system: most things is an object, so a lot of objects are constantly spawned and torn down, often in rapid succession because the compiler/interpreter can make few hard analyses of when stuff is needed. Python also has a high function-call overhead. > | So far the only way to scale properly with Zope is a combination of > | a load-balancing clustering system (eg., TurboLinux' TurboCluster > | Server, which I can personally vouch for -- brilliant stuff -- or > | Linux Virtual Server) with Digital Creations' ZEO, of which I've > | only read about. > > I actually thought of ZEO as a very nice way to scale Zope. I agree. > | There are Zope sites out there that are suffering scalability > | problems (I won't mention specifics, other than that the project I'm > | involved in is one of them). > > It would be very much appreciated if you could share some specifics. No. Ask around, do some research. Ask Digital Creations -- they probably know of a few, although I'm guessing that they might feel it would hurt their reputation to tell. Many companies using Zope might not want to tell you because it would hurt their position, especially if they're public companies. Here's one specific case that I'm personally struggling with. I have a page that returns a large number of dynamic database results in a relatively simple table. The results are first munged by a small Python script. This stuff is slow. Internally, as far as I can determine (through shallow study of the database code), Zope allocates a row object for every row you access -- even if the row has been returned earlier on. Zope has a 1-row cache for cases when you repeatedly ask for the same row in succession. Zope also has a row cache that is useful for static result sets. Yet, for dynamic result sets, the processing overhead is huge. The overhead isn't so higher than any other overhead in other areas in Zope, but it's especially painful here, because it affects the generation time of a single page, whereas other kinds of overhead are more evenly distributed across multiple pages and multiple users. > [...] > | As far as pollution goes, assuming Zope exports the appropriate data > | -- in whatever form -- then support for > | performance/monitoring/management APIs such as SNMP, PCP, WBEM, and > | to a lesser extent PDH, aren't difficult to isolate into add-on > | products. > > You are right about that, and I think that's a better way to provide > such support, rather then building specific support for any of them > into Zope. Exactly. However, the necessary counters must be built into Zope at some point, and exposed through a common (XML? Python/XML-RPC?) API. Then we could attach publishers for SNMP, HTML, XML, whatever. Which reminds me. Does Zope have a mechanism for extending the Control_Panel namespace other than through the Product sub-folder? I'm too lazy to check, and I don't remember if this was ever discussed. -- Alexander Staubo http://alex.mop.no/ "`Ford, you're turning into a penguin. Stop it.'" --Douglas Adams, _The Hitchhiker's Guide to the Galaxy_

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manage_exportObject
by Daniel G. Rusch 07 Mar '00

07 Mar '00

Now I am desperate, this is the fourth posting and still only one reply. Any thoughts no matter how far fetched would be overwhelmingly appreciated. Does anyone know how to export an object (Folder or such) from outside of the Folder that contains the item to be exported without hard coding the path. In other words I would like to be able to have a user interface which would allow a person, with an export role, to be able to enter a list of fully qualified Items to be exported. Consider: FolderA FolderB ItemToExport I can export ItemToExport from FolderA by calling: <dtml-with "FolderA.FolderB"> <dtml-call "manage_exportObject(id='ItemToExport')"> </dtml-with> but I don't want the FolderA.FolderB to be hard coded. I would like it to be a var that I pass into the method. Something like: <dtml-with FullPath> what should the syntax be. Thanks,

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Syntax for getting property sheet
by Jon Prettyman 07 Mar '00

07 Mar '00

If I have a ZClass with a property sheet called 'Info', how can I get access to the sheet when I DON'T have an instance of that ZClass to work with. Specifically, I want an ADD form for my ZClass that has an ID field and a dynamically generated section containing all the properties from 'Info' all on ONE from. I can't seem to figure out how to dynamically generate the property section without an instance to work with. -Jon

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newbie tree q - how collapse and expand
by Andy Heath 07 Mar '00

07 Mar '00

I'm getting better but stil learning. I want to collapse/expand a tree at will so that I can come in from particular hyperlinks to a known tree state. I know there are two variables I can set but I don't know how to do this from code. For example how could I have a hyperlink whose HREF is a page containing a tree in such a way that when you get there the tree gets collapsed while another link to the same page doesn't collapse it. Can someone show me some code that dows this please. Andy -- ------------------------------------------------- Andy Heath a.k.heath(a)open.ac.uk The Open University +44 (0) 114 2885738

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Tricky usage of string to integer conversion
by Brian K. Holdsworth 07 Mar '00

07 Mar '00

I am trying to do the following: <dtml-let x:int="REQUEST.get('prod_config')" item="_[REQUEST.get('prod_id')]" price="item.price_list[x]"> <INPUT type="hidden" name="chargetotal" value="<dtml-var price>"> </dtml-let> The prod_config variable is a number (returned as a string) from a SELECT list. The prod_id variable is the id of an object in the same folder as this method that has a price_list attribute. price_list is a list of strings representing prices. This results in a "Name Error" where Zope cannot find "x". If I change line 3 to this: price="item.price_list['x']"> it fixes the Name Error, but then I get a "Sequence Index must be an integer" error on price_list['x']. I would have thought the use of "x:int" in my <dtml-let> would take care of this issue. Seems I can't win! Does anyone know the correct way to do this lookup? Best Regards, Brian Holdsworth

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AUTHENTICATED_USER.getUserName()
by Shaw, Mark 07 Mar '00

07 Mar '00

Hello, Is there a HOW-TO or other documentation that shows how to set up a login page so that you can use AUTHENTICATED_USER.getUserName()? Thanks in advance for any help/pointers provided. -Mark

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Very Newbie Questions
by Tom Scheidt 07 Mar '00

07 Mar '00

This is day 2 with Zope for me: 1. On page 20 of the Zop Content Managers Guide it says "Create a folder under Research with the "id" home and the name "Products Home Page". Im assuming they meant to say "Creat a folder under Products", not Research. 2. If I make a 2 folders within the same folder and one is called images, the other html, the DTML methods calling the images from the html folder wont work because they must be in a subfolder of the images folder. Is there a way to get around this? to have the images and html in seperate folders? 3. In the Zope Content Managers Guide, under the "Creating a Configuration Interface", I am getting an error message when I test the form page called "Home Page Designer". It askes for my username and password then says: Zope Error Zope has encountered an error while publishing this resource. Unauthorized You are not authorized to access manage_changeProperties. ************************* Tom Scheidt www.falsemirror.com tom(a)falsemirror.com *************************

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RE: [Zope] Gaining Enlightenment
by dale w lance 07 Mar '00

07 Mar '00

> -----Original Message----- > From: jiva [mailto:jiva@devware.com] > Sent: Tuesday, March 07, 2000 11:11 AM > To: richard > Cc: jiva; zope > Subject: Re: [Zope] Gaining Enlightenment > > > I don't claim to be an OO master or a ZOPE master, but I'll give this > a shot anyway and share some recent revelations I have had about OO in > general. > > First off, the examples that people always use to demonstrate OO > concepts wind up being more distracting than they are worth. For > instance modeling a can of spam in OO. That would be a logical thing > to do, if you were writing a control program for a can of spam. But Actually the guys at Spam inc. IT do model Spam cans (how about the lot numbers in case of botulism or something?) I believe the reference to Spam was just an example though ;-) > NOT if you were writing a database app! This, I think is one of the > most confusing parts for database programmers coming to OO. > > Second, so if you don't model your can of spam, then what DO you > model? Well, you model *your data* and if your data is a database, > then that's what you model! Soo, you create an object of type > "Products_Table" which contains methods to operate on the entire More likely I would write a Class called "Table" that knows about accessing all relational database tables not just "Products" (see Data Adapters in Zope) > table. Then you create objects of types "Products" which contain > methods to operate on the objects. But since your products can be > many different kinds, you don't "hard code" what kind of product they > are, you just make a generic object that contains generic functions. > If you wind up needing to do something special for a particular > product, *then* you create a subclass of product for that kind of > product that you can use for that. Ie: "Delicate_Product" might be a > subclass of "Product" that might have a special some special methods Would you have a different table for this? This is a debatable topic - if you don't have different attributes for your subclass then, it is argued, you don't really need that subclass. Special methods for this can be done as you propose or just tested for in one class. The reason this is important here (in this discussion) has to do with oo-relational mismatch or impedance. When you are bringing back your objects from the database you are going to have to know which object to "instantiate" (this term is used losely here). This means special handling for your queries. Or you can pay the pain by having two tables which makes your queries for all objects harder. As you can see it isn't necessarily simple. > for dealing with products of that type. Something like "find" should > be a method of the table that returns an instance of your product. > > So, your loop becomes something like this (pseudo code that looks like > c++?): > > while(sData = Input.Read()) > { > MyProduct = new Product(sData); // object init's itself // here you would need to test what kind of Product it is // just before instantiation > if(MyProduct.Validate()) > { > MyProduct.Write(Table); > } > delete MyProduct; > } > > On Tue, Mar 07, 2000 at 09:47:21AM +0000, Richard Moon wrote: > > Dear Zopers, > > > > I read Chris McDonough's How To on Gaining Zope > Enlightenment by Grokking > > Object Orientation. ------------------ Snip! -------------------------------- > > Chris, > > I enjoyed your How-To on Gaining Enlightenment very much. > I've been using > > Zope for a couple of months now and I've made some progress > - my first > > project has been to use it to give access to established > databases over an > > Intranet. Like you I think its wonderful, but like you I > keep getting > > stuck. Never mind, with the help of the mailing lists and > long hours > > reading books on Python etc I've made progress. > > BUT ... (there's always a but isn't there) - no matter how > much I read and > > play around with OO - I still don't 'get it'. My background > is many years > > working with relational databases on Unix - (and there are > thousands like me). > > I just don't get the bit about storing data as objects. > Could we discuss > > this a bit more and perhaps publish my questions and your > answers on > > Zope.org ?? This may help me and the thousands like me. > > OK, you create your class of Spam, which has attributes of > cansize and > > texture and it has methods that display these attributes. > No doubt you > > could add other attributes, such as selling price and > develop a method to > > increase the price by a percentage. OK so far ? Yes this is OK > > Now we create an object (which is an instance of the class > Spam) - which we > > call myfirstcan. We can define the attributes for that > object when we > > create it or later and we can use the methods defined in > the Spam class to > > do so. OK so far ? Yep > > > > What I don't get is how you store and retrieve the objects > you create. There are several ways actually -- Lets use a simple approach, One Class <--> One Table > > Let's go to a more realworld example - how would you > implement a stock > > system using objects ? Let's take the simple table Stock > which has three > > columns > > Product_code Description Price > > and we could enter rows of data into it, for example - > > ABC Spluggifier 20.00 > > CDE Super-spluggifier 25.00 This would translate to a "Stock" object with three attributes as you have stated below - > > > > Now if I was writing a conventional database system I would > maintain the > > above by defining a program which perhaps prompted the user for the > > required columns (Product, Description,Price) and then I > would store the > > users input in a row in a table. Perhaps another program > (the price change > > program) would use a stored procedure to allow price change. OK ? Yes this is still olde kinderhook. > > Now in OO terms I see that I could create a class of Stock > with attributes > > Product, Description and Price. I could create a method to > allow price > > changes. Very neat. For me this method would be an instance method, each instance would have it called upon itself. > > Then I can create an object( i.e a particular stock item) by saying > > something like > > product_1 = Stock(product_code="ABC", > Description="Spluggifier", Price-"20.00") > > Now I can create another object by saying > > product_2 = etc > > but that is not the way you would do it surely. You would > be effectively > > 'hard-coding' each product in your system. > > Surely you would have a program which did something like > > WHILE the user is entering data > > PROMPT user for data > > VALIDATE data > > WRITE data to database > > END WHILE > > How do you do that in OO terms ? Actually you are correct. There will be an input program. You won't see much difference between OO and your conventional database way (if you will allow me to assign that term here). The reason is we haven't actually done anything too significant yet. > > How then do you search and retrieve an object with a > particular value of > > product_code ? Using my assumptions and examples from above I would have the Stock class ask my table class to build a SQL query to do this > > How do you write a program which updates the price of all > stock items where > > the product_code begins with AB by 2%.? As above have the Stock Class have the table class find all "rows" which meet this criteria then for each instance send updatePriceBy(2) where the 2 is an argument and since it is positive the instance of stock will add 2% to its own price > > Thanks for reading this far. Hope you can stop my head spinning ! > > Here comes more spin though I'm afraid (sorry :-P) Up til now I've left out alot of the mechanics. The Table Object knows how to form SQL queries which gets you subsets of your objects (not just rows of data) It in effect provides the code: product_1 = Stock(product_code="ABC",Description="Spluggifier", Price-"20.00") only instead of product_1 it would be 'next_row' or 'this_row' (depending on how you like to think of database cursors). Also somewhere there is a mapping between the Table and the Class it represents. This allows the Table to become a Class, the row to become an instance, and the columns to be attributes. These mappings would be plugged into the above code also (i.e. product_code becomes attributes[1]) This mapping solution is a common pattern - IDL to Corba, DTD to XML in generic terms. Here we start to see OO work. I defined my class and map it to different things such as Corba or XML - now I can ship the object flattened as a string (or some other form) and a reciever can inflate it back. This would be the user input form. This flattening has a special name in ZODB (as far as I can tell) it's "pickling" Hope this doesn't add more head spin. There is much more to this story, we haven't even talked about, such as foreign keys and how to map them to Objects. As far as modeling the data, I don't model a database, just the data, but it also depends on if you are supporting a previously existing database or starting new. I have done both and it is a black art. You have to support management, other departments etc without tipping the boat over, so you generally follow the flow. But for the most part you want to analyze the problem domain from an object point of view from the start. This gives you important insights to other parts of the problem such business processes and object interactions you didn't know about. OO is not just an elaborate ERD (Entity Relationship Diagram) But it is the most common place to start. This is just one way to do it, not necessarily the "Right" way, (if there is such a thing) Hope this Helps Dale

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browser detection
by daniel edmond greenlaw 07 Mar '00

07 Mar '00

is it possible to do browser detection with zope? if so, how? daniel

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empty multiple lists
by Ingo Assenmacher 07 Mar '00

07 Mar '00

Hi everybody, although this may have been discussed several times: I added a multiple property to a class, but when I call the instance's property sheet from the management interface, I get an Type Error, whenever I did not chose anything from the selection box. That is of course ok, because there is no property defined within the instance if I did not select anything. (getProperty(id) fails on None) How do I create an "empty selection"? Thanks for your help BTW: <dtml-call "REQUEST.set('x','[]')"> did not work.

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