[mod_python] PSP/Mac OS X line ending gotcha

Jim Gallacher jpg at jgassociates.ca
Sat Apr 29 14:37:20 EDT 2006

Jeffrey A. Zelt wrote:
> I've only just started using mod_python, so please excuse this if it is 
> documented in an obvious place.  Let me put it very simply.  On Mac OS 
> X, make sure that your HTML files are terminated by :
>    a line feed (ascii 10) and NOT a carriage return (ascii 13).
> The Windows line ending of CRLF is also OK because it includes the line 
> feed.  PSP does *not* like lines terminated by only a carriage return.  
> Here is how I encountered this.  It should also indicate when you should 
> look out for this issue.
> I successfully implemented some functionality through a custom generic 
> python handler - that went pretty smoothly.  Then I wanted to use PSP 
> for simple templating.  Everything worked perfectly when I first 
> introduced python expressions delimited by:
>    ‘<%=’  and  ‘%>’
> However, as soon as I tried using python code delimited by:
>    ‘<%’  and  ‘%>’
> all hell broke loose and I could not get anything to work.  A simplified 
> version of what I was trying was something like:
>     <%
>    for i in range(n):
>        # start for loop
>    %>
>         HTML code to repeat n times
>    <%
>    # terminate for loop
>    %>
> This just repeats the block of HTML code n times.  The details of the 
> python code here are not important.  This construction triggered various 
> errors, depending on the details of the python code I inserted into the 
> page.  The problem was that I was using Adobe GoLive to edit my web 
> pages and to insert the python code in the page (I am talking about the 
> source view, not the WYSIWYG/Layout view).  My version of GoLive is a 
> little old and still prefers to write files with carriage return line 
> endings.  This was the default for the Mac OS before Mac OS X.  
> Everything *looks* OK in the GoLive editor and it also looked OK in the 
> other editors I chose to check the code (other editors would have tipped 
> me off, but I did not use one of those).
> However, it seems that the PSP engine, or whatever you want to call it, 
> does not treat carriage returns as line endings, and therefore chokes 
> badly when encountering code written this way.

The psp parser expects lines of python code to end in:

\r\n | \n | %>

So using \r as the line terminator will indeed mess things up.

> GoLive has a menu item where you can select  the desired line 
> terminator.  I selected "Unix (LF)".  This made no visible change to the 
> document when viewed in GoLive, but then suddenly the <% ... %> PSP 
> parts of the document worked perfectly.
> It is probably obvious when you think about it, but it is tricky to 
> detect if you are bit by it because you may not visibly see anything 
> wrong with the code you are editing.
> I hope this helps someone avoid what I went through.

It should be easy enough to fix this. At the very least it should be 

I'll file a bug report. Thanks for your input.

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