Hi James, I'd really like to help you out with ZPatterns. However, I'm finding it very hard work to make sense of your emails to zope-dev. I only have a certain amount of time to keep up with mailing lists, and so I usually just skip messages that are hard to read. I'm replying to the list as well, and I hope you don't mind. I'm hoping that it might give others some hints on writing easily understood emails. Please understand that I really want to help with the software. This is the essential first step towards that. With that said, let's take a look at your message. James Johnson wrote:

another person had this problem earlier. It may have been because they used quotes like <dtml-var "foo">. It should be <dtml-var foo>. I get the same keyerror on foo?. I actually had ended up with the code you just gave from previous post. There must be a problem if others have had keyerrors. My understanding is that by placing the skinscript in the specialist would be a blackbox thing and placing it in the specialists rack with the other providers would be a whitebox thing. So seeing that the index_html is a method of the Class folder is should "see" the artist property. So I need to call the specialist and do a propertyMap() or something on it first? What could cause a keyerror? Seems to me that myPPS has no keys because its empty. I'm using win98,winNT4, win2000, redhat 6.2, zope 2.2.1, ZPatterns 4.2.2Alpha or the latest. I to work all of the platforms. For the most part it's going to to be the win98 platform I'm developing on. I can't wait to pump out my first ZPattern product.

You've sent the email as one big paragraph. I can read it better if you can separate it out into several paragraphs that form chunks of related information. The information is tightly coupled within a paragraph; the paragraphs are related to each other less strongly. This is just like writing good software. Let's look through your message bit by bit. Here, I'll try and answer your questions.

another person had this problem earlier.

You didn't quote any context from previous messages, and just started the message with a reference to "this problem". Well, there may be a few different problems going on, all at once. In some senses, they might be the same problem, but seen from different angles, or viewed at different levels of abstraction. For example, sometimes I might ask for help with a problem. I think I have a syntax error in my code. However, whilst it is true that I have a syntax error, people are able to also tell me that I'm going about something in a way that is unnecessarily complex. The answer is to quote a few lines from the email you're replying to, and also to restate the problem so that it is clear to everyone exactly what it is you are talking about. This is also an opportunity to clarify your own thoughts on what seems to be going on with your software. I find this step invaluable, and sometimes, the extra clarity I get from it shows me something I missed before, and I end up solving the problem myself, and sharing a successful solution with the mailing list.

It may have been because they used quotes like <dtml-var "foo">. It should be <dtml-var foo>.

When you're talking about code, you should include a small example, even if it means pasting it in from a previous email. Otherwise, I can't tell whether what you say makes sense. In what you have written, above, I can't tell whether <dtml-var "foo"> or <dtml-var foo> is best. In general, I use both of those forms, and others, in different situations. There is always a reason why I'd use one or the other.

I get the same keyerror on foo?.

Is this a question that you want me to answer? Actually, I don't understand what you are saying or answering here. If you get an error from some code, and you want people to help you understand why you get the error, you should include all the code that causes the error. If there is a lot of code, take the time to produce a small example that exhibits the same error. Then, others can easily try out what you have done, and it's more likely that someone will be able to help you with a solution. Also, if you get an error, and you don't understand why, include the name of the error, and the error value that Zope tells you. Also, include the traceback. An error doesn't just occur on its own. It is part of a story, and it only occurs when you do things a certain way. In order for people to understand what you have done to get the error, you need to tell the story. Start by saying what the versions of software on your system are, as some problems are caused by using old or incompatible software. I see you've done that below. It is generally better if it is at the start, as it gives your readers some context for reading the rest of the story. Next, explain briefly what you are trying to do. If you don't do this, some of the answers people give won't apply in your circumstances. As a silly example, if I thought your goal is to have a bug-free Zope system, and you are having problems with ZPatterns, I could recommend that you just erase ZPatterns, and all the related objects. There, problem solved :-) But, even in less silly examples, readers need to know what you want to achieve. Ok, so you've described your Zope installation, and you've stated clearly and briefly what it is you're trying to do. Next, tell the story of how you have got to the point that the error occurs, and try to explain why you chose to do it the way you did. Again, this helps people to make suggestions that will work for you. For example: "I want to make a CD library using ZPatterns. This is some software that allows me to store the names and tracks of the CDs I own, search for a particular CD by name or track, and browse them in alphabetical order. "First, I created a ZClass called CD that is derived from DataSkin and ObjectManager. Then I created another ZClass called Track that is just derived from DataSkin. I checked the box to say that they should be derived from the usual base classes for persistence. I created both inside a Product I called CDLibrary. The CDs will live under a customizer folder, in subfolders representing styles of music, and the tracks will be sub-objects of the CDs. "Next, I created a Folder w/ Customizer Support in the root of my Zope, called CompactDisks. I went to its Customizers tab, and added a customizer called customize_cds and another called customize_tracks." Keep going until you have described what you've done and why, and what you did to get the error, and what you were trying to do when you got the error. Errors are tricky things, and sometimes they're caused by something you did, or something you didn't do and should have, in a different part of the system than you were working on when you first saw the error.

I actually had ended up with the code you just gave from previous post.

That's great. Where did you put it? Did it work? Was it exactly the same code? It is usually best to post small examples of the code you're using.

There must be a problem if others have had keyerrors.

I'm confused here. What do you do to make a keyerror occur?

My understanding is that by placing the skinscript in the specialist would be a blackbox thing and placing it in the specialists rack with the other providers would be a whitebox thing.

Well, that depends. One way of looking at it is that Data-PlugIns that you put in a Rack apply only to Objects stored in that Rack, whereas Data-PlugIns that you put directly in the specialist apply to all the objects in all the Racks in that specialist. Racks are mostly about storage. So, I'd put SkinScript that is to do with storage in Racks. However, cataloguing objects' metadata in a ZCatalog is something you'd want to do regardless of how something is stored, so I'd generally put a CatalogTrigger in the Specialist. Also, if you wanted to be sent an email whenever on object in the specialist is deleted, well, put some SkinScript in the Specialist for that. Of course, the SkinScript can't send an email; it'll call a different method for that.

So seeing that the index_html is a method of the Class folder is should "see" the artist property. So I need to call the specialist and do a propertyMap() or something on it first? What could cause a keyerror? Seems to me that myPPS has no keys because its empty.

I can't make much sense of this paragraph. Be wary of using abbreviations like myPPS, and assuming that readers will understand what kind of object it is. When you are asking a question, don't ask it as a statement; it is difficult to know exactly what the question means to you.

So I need to call the specialist and do a propertyMap() or something on it first?

If you mean "Do I need to call the propertyMap method of the specialist before... ?", then say that. And when you say "...on it first?" I'm not sure what you want to achieve by calling propertyMap(), so I don't know what you'd want to do after calling it. Sometimes it is useful if you can instrument your code. That is, you print out the value of particular variables at various points in your program. You can then say "I call method foo of the specialist, and I expect to get back a PropertySheet, but it returns None instead." A clear way of describing a problem is to say what you expect to happen, and what really happens, and how they two are different.

I'm using win98,winNT4, win2000, redhat 6.2, zope 2.2.1, ZPatterns 4.2.2Alpha or the latest. I to work all of the platforms. For the most part it's going to to be the win98 platform I'm developing on.

Ok. This really belongs earlier on, but I'm glad you've included it anyway. In this case, I think you only need to say what version of Zope and what version of ZPatterns you're using. However, if you're being complete, state your operating system, and its version, the version of Python you're using, and whether you installed it as a binary, or from source, the version of Zope, and whether it is from a binary or from source, and the version of ZPatterns. When you talk about the operating system, say just what operating system you are using to do your development on right now. If you are really simultaneously working and testing on Windows 98, NT4, 2000 and RedHat linux 6.2, then that's fine. Otherwise, just say the system you're actually getting the error on.

I can't wait to pump out my first ZPattern product.

This stuff should be fun. Looks like you have a positive approach to learning this stuff. Great! If you have an IRC client, you might want to drop in on irc.zope.net #zope sometime. Various people who are knowledgeable about Zope and ZPatterns use IRC there from time to time. Sometimes they'll have time to help out with problems. -- Steve Alexander Software Engineer Cat-Box limited http://www.cat-box.net