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diff --git a/docs/users_guide_2_src/C_comparisions.txt b/docs/users_guide_2_src/C_comparisions.txt new file mode 100755 index 0000000..56a0fb3 --- /dev/null +++ b/docs/users_guide_2_src/C_comparisions.txt @@ -0,0 +1,451 @@ +\section{Cheetah vs. Other Template Engines} +\label{comparisons} + +This appendix compares Cheetah with various other template/emdedded scripting +languages and Internet development frameworks. As Cheetah is similar to +Velocity at a superficial level, you may also wish to read comparisons between +Velocity and other languages at +\url{http://jakarta.apache.org/velocity/ymtd/ymtd.html}. + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\subsection{Which features are unique to Cheetah} +\label{comparisons.unique} + +\begin{itemize} +\item The {\bf block framework} (section \ref{inheritanceEtc.block}) +\item Cheetah's powerful yet simple {\bf caching framework} (section + \ref{output.caching}) +\item Cheetah's {\bf Unified Dotted Notation} and {\bf autocalling} + (sections \ref{language.namemapper.dict} and + \ref{language.namemapper.autocalling}) +\item Cheetah's searchList (section \ref{language.searchList}) + information. +\item Cheetah's \code{\#raw} directive (section \ref{output.raw}) +\item Cheetah's \code{\#slurp} directive (section \ref{output.slurp}) +\item Cheetah's tight integration with Webware for Python (section + \ref{webware}) +\item Cheetah's {\bf SkeletonPage framework} (section + \ref{libraries.templates.skeletonPage}) +\item Cheetah's ability to mix PSP-style code with Cheetah + Language syntax (section \ref{tips.PSP}) + Because of Cheetah's design and Python's flexibility it is + relatively easy to extend Cheetah's syntax with syntax elements from almost + any other template or embedded scripting language. +\end{itemize} + +%% @@MO: What about the new features we've been adding? + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\subsection{Cheetah vs. Velocity} +\label{comparisons.velocity} + +For a basic introduction to Velocity, visit +\url{http://jakarta.apache.org/velocity}. + +Velocity is a Java template engine. It's older than Cheetah, has a larger user +base, and has better examples and docs at the moment. Cheetah, however, has a +number of advantages over Velocity: +\begin{itemize} +\item Cheetah is written in Python. Thus, it's easier to use and extend. +\item Cheetah's syntax is closer to Python's syntax than Velocity's is to +Java's. +\item Cheetah has a powerful caching mechanism. Velocity has no equivalent. +\item It's far easier to add data/objects into the namespace where \$placeholder + values are extracted from in Cheetah. Velocity calls this namespace a 'context'. + Contexts are dictionaries/hashtables. You can put anything you want into a + context, BUT you have to use the .put() method to populate the context; + e.g., + +\begin{verbatim} +VelocityContext context1 = new VelocityContext(); +context1.put("name","Velocity"); +context1.put("project", "Jakarta"); +context1.put("duplicate", "I am in context1"); +\end{verbatim} + + Cheetah takes a different approach. Rather than require you to manually + populate the 'namespace' like Velocity, Cheetah will accept any existing + Python object or dictionary AS the 'namespace'. Furthermore, Cheetah + allows you to specify a list namespaces that will be searched in sequence + to find a varname-to-value mapping. This searchList can be extended at + run-time. + + If you add a `foo' object to the searchList and the `foo' has an attribute + called 'bar', you can simply type \code{\$bar} in the template. If the + second item in the searchList is dictionary 'foofoo' containing + \code{\{'spam':1234, 'parrot':666\}}, Cheetah will first look in the `foo' + object for a `spam' attribute. Not finding it, Cheetah will then go to + `foofoo' (the second element in the searchList) and look among its + dictionary keys for `spam'. Finding it, Cheetah will select + \code{foofoo['spam']} as \code{\$spam}'s value. + +\item In Cheetah, the tokens that are used to signal the start of + \$placeholders and \#directives are configurable. You can set them to any + character sequences, not just \$ and \#. +\end{itemize} + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\subsection{Cheetah vs. WebMacro} +\label{comparisons.webmacro} + +For a basic introduction to WebMacro, visit +\url{http://webmacro.org}. + +The points discussed in section \ref{comparisons.velocity} also apply to the +comparison between Cheetah and WebMacro. For further differences please refer +to \url{http://jakarta.apache.org/velocity/differences.html}. + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\subsection{Cheetah vs. Zope's DTML} +\label{comparisons.dtml} + +For a basic introduction to DTML, visit +\url{http://www.zope.org/Members/michel/ZB/DTML.dtml}. + +\begin{itemize} +\item Cheetah is faster than DTML. +\item Cheetah does not use HTML-style tags; DTML does. Thus, Cheetah tags are + visible in rendered HTML output if something goes wrong. +\item DTML can only be used with ZOPE for web development; Cheetah can be + used as a standalone tool for any purpose. +\item Cheetah's documentation is more complete than DTML's. +\item Cheetah's learning curve is shorter than DTML's. +\item DTML has no equivalent of Cheetah's blocks, caching framework, + unified dotted notation, and \code{\#raw} directive. +\end{itemize} + +Here are some examples of syntax differences between DTML and Cheetah: +\begin{verbatim} +<ul> +<dtml-in frogQuery> + <li><dtml-var animal_name></li> +</dtml-in> +</ul> +\end{verbatim} + +\begin{verbatim} +<ul> +#for $animal_name in $frogQuery + <li>$animal_name</li> +#end for +</ul> +\end{verbatim} + +\begin{verbatim} +<dtml-if expr="monkeys > monkey_limit"> + <p>There are too many monkeys!</p> +<dtml-elif expr="monkeys < minimum_monkeys"> + <p>There aren't enough monkeys!</p> +<dtml-else> + <p>There are just enough monkeys.</p> +</dtml-if> +\end{verbatim} + +\begin{verbatim} +#if $monkeys > $monkey_limit + <p>There are too many monkeys!</p> +#else if $monkeys < $minimum_monkeys + <p>There aren't enough monkeys!</p> +#else + <p>There are just enough monkeys.</p> +#end if +\end{verbatim} + +\begin{verbatim} +<table> +<dtml-in expr="objectValues('File')"> + <dtml-if sequence-even> + <tr bgcolor="grey"> + <dtml-else> + <tr> + </dtml-if> + <td> + <a href="&dtml-absolute_url;"><dtml-var title_or_id></a> + </td></tr> +</dtml-in> +</table> +\end{verbatim} + +\begin{verbatim} +<table> +#set $evenRow = 0 +#for $file in $files('File') + #if $evenRow + <tr bgcolor="grey"> + #set $evenRow = 0 + #else + <tr> + #set $evenRow = 1 + #end if + <td> + <a href="$file.absolute_url">$file.title_or_id</a> + </td></tr> +#end for +</table> +\end{verbatim} + +The last example changed the name of \code{\$objectValues} to +\code{\$files} because that's what a Cheetah developer would write. +The developer would be responsible for ensuring \code{\$files} returned a +list (or tuple) of objects (or dictionaries) containing the attributes (or +methods or dictionary keys) `absolute\_url' and `title\_or\_id'. All these +names (`objectValues', `absolute\_url' and `title\_or\_id') are standard parts +of Zope, but in Cheetah the developer is in charge of writing them and giving +them a reasonable behaviour. + +Some of DTML's features are being ported to Cheetah, such as +\code{Cheetah.Tools.MondoReport}, which is based on the +\code{<dtml-in>} tag. We are also planning an output filter as flexible as +the \code{<dtml-var>} formatting options. However, neither of these are +complete yet. + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\subsection{Cheetah vs. Zope Page Templates} +\label{comparisons.zpt} + +For a basic introduction to Zope Page Templates, please visit +\url{http://www.zope.org/Documentation/Articles/ZPT2}. + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\subsection{Cheetah vs. PHP's Smarty templates} +\label{comparisons.smarty} + +PHP (\url{http://www.php.net/}) is one of the few scripting languages +expressly designed for web servlets. However, it's also a full-fledged +programming language with libraries similar to Python's and Perl's. The +syntax and functions are like a cross between Perl and C plus some original +ideas (e.g.; a single array type serves as both a list and a dictionary, +\verb+$arr[]="value";+ appends to an array). + +Smarty (\url{http://smarty.php.net/}) is an advanced template engine for +PHP. ({\em Note:} this comparision is based on Smarty's on-line documentation. +The author has not used Smarty. Please send corrections or ommissions to the +Cheetah mailing list.) Like Cheetah, Smarty: + +\begin{itemize} +\item compiles to the target programming language (PHP). +\item has configurable delimeters. +\item passes if-blocks directly to PHP, so you can use any PHP expression in +them. +\item allows you to embed PHP code in a template. +\item has a caching framework (although it works quite differently). +\item can read the template definition from any arbitrary source. +\end{itemize} + +Features Smarty has that Cheetah lacks: +\begin{itemize} +\item Preprocessors, postprocessors and output filters. You can emulate a +preprocessor in Cheetah by running your template definition through a filter +program or function before Cheetah sees it. To emulate a postprocessor, run a +.py template module through a filter program/function. To emulate a Smarty +output filter, run the template output through a filter program/function. If +you want to use ``cheetah compile'' or ``cheetah fill'' in a pipeline, use +\code{-} as the input file name and \code{--stdout} to send the result to +standard output. Note that Cheetah uses the term ``output filter'' differently +than Smarty: Cheetah output filters (\code{\#filter}) operate on placeholders, +while Smarty output filters operate on the entire template output. There has +been a proposed \code{\#sed} directive that would operate on the entire output +line by line, but it has not been implemented. +\item Variable modifiers. In some cases, Python has equivalent string +methods (\code{.strip}, \code{.capitalize}, \code{.replace(SEARCH, REPL)}), +but in other cases you must wrap the result in a function call or write +a custom output filter (\code{\#filter}). +\item Certain web-specific functions, which can be emulated with +third-party functions. +\item The ability to ``plug in'' new directives in a modular way. Cheetah +directives are tightly bound to the compiler. However, third-party +{\em functions} can be freely imported and called from placeholders, and +{\em methods} can be mixed in via \code{\#extends}. Part of this is +because Cheetah distinguishes between functions and directives, while +Smarty treats them all as ``functions''. Cheetah's design does not +allow functions to have flow control effect outside the function +(e.g., \code{\#if} and \code{\#for}, which operate on template body lines), +so directives like these cannot be encoded as functions. +\item Configuration variables read from an .ini-style file. The +\code{Cheetah.SettingsManager} module can parse such a file, but you'd +have to invoke it manually. (See the docstrings in the module for +details.) In Smarty, this feature is used for +multilingual applications. In Cheetah, the developers maintain that everybody +has their own preferred way to do this (such as using Python's \code{gettext} +module), and it's not worth blessing one particular strategy in Cheetah since +it's easy enough to integrate third-party code around the template, or to add +the resulting values to the searchList. +\end{itemize} + +Features Cheetah has that Smarty lacks: +\begin{itemize} +\item Saving the compilation result in a Python (PHP) module for quick +reading later. +\item Caching individual placeholders or portions of a template. Smarty +caches only the entire template output as a unit. +\end{itemize} + +Comparisions of various Smarty constructs: +\begin{verbatim} +{assign var="name" value="Bob"} (#set has better syntax in the author's opinion) +counter (looks like equivalent to #for) +eval (same as #include with variable) +fetch: insert file content into output (#include raw) +fetch: insert URL content into output (no euqivalent, user can write + function calling urllib, call as $fetchURL('URL') ) +fetch: read file into variable (no equivalent, user can write function + based on the 'open/file' builtin, or on .getFileContents() in + Template.) +fetch: read URL content into variable (no equivalent, use above + function and call as: #set $var = $fetchURL('URL') +html_options: output an HTML option list (no equivalent, user can + write custom function. Maybe FunFormKit can help.) +html_select_date: output three dropdown controls to specify a date + (no equivalent, user can write custom function) +html_select_time: output four dropdown controls to specify a time + (no equvalent, user can write custom function) +math: eval calculation and output result (same as #echo) +math: eval calculation and assign to variable (same as #set) +popup_init: library for popup windows (no equivalent, user can write + custom method outputting Javascript) + + +Other commands: +capture (no equivalent, collects output into variable. A Python + program would create a StringIO instance, set sys.stdout to + it temporarily, print the output, set sys.stdout back, then use + .getvalue() to get the result.) +config_load (roughly analagous to #settings, which was removed + from Cheetah. Use Cheetah.SettingsManager manually or write + a custom function.) +include (same as #include, but can include into variable. + Variables are apparently shared between parent and child.) +include_php: include a PHP script (e.g., functions) + (use #extends or #import instead) +insert (same as #include not in a #cache region) +{ldelim}{rdelim} (escape literal $ and # with a backslash, + use #compiler-settings to change the delimeters) +literal (#raw) +php (``<% %>'' tags) +section (#for $i in $range(...) ) +foreach (#for) +strip (like the #sed tag which was never implemented. Strips + leading/trailing whitespace from lines, joins several lines + together.) + + +Variable modifiers: +capitalize ( $STRING.capitalize() ) +count_characters ( $len(STRING) ) +count_paragraphs/sentances/words (no equivalent, user can write function) +date_format (use 'time' module or download Egenix's mx.DateTime) +default ($getVar('varName', 'default value') ) +escape: html encode ($cgi.escape(VALUE) ) +escape: url encode ($urllib.quote_plus(VALUE) ) +escape: hex encode (no equivalent? user can write function) +escape: hex entity encode (no equivalent? user can write function) +indent: indent all lines of a var's output (may be part of future + #indent directive) +lower ($STRING.lower() ) +regex_replace ('re' module) +replace ($STRING.replace(OLD, NEW, MAXSPLIT) ) +spacify (#echo "SEPARATOR".join(SEQUENCE) ) +string_format (#echo "%.2f" % FLOAT , etc.) +strip_tags (no equivalent, user can write function to strip HTML tags, + or customize the WebSafe filter) +truncate (no equivalent, user can write function) +upper ($STRING.upper() ) +wordwrap ('writer' module, or a new module coming in Python 2.3) +\end{verbatim} + +Some of these modifiers could be added to the super output filter we +want to write someday. + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\subsection{Cheetah vs. PHPLib's Template class} +\label{comparisons.php} + +PHPLib (\url(http://phplib.netuse.de/) is a collection of classes for various +web objects (authentication, shopping cart, sessions, etc), but what we're +interested in is the \code{Template} object. It's much more primitive than +Smarty, and was based on an old Perl template class. In fact, one of the +precursors to Cheetah was based on it too. Differences from Cheetah: + +\begin{itemize} +\item Templates consist of text with \code{\{placeholders\}} in braces. +\item Instead of a searchList, there is one flat namespace. Every variable + must be assigned via the \code{set\_var} method. However, you can pass + this method an array (dictionary) of several variables at once. +\item You cannot embed lookups or calculations into the template. Every + placeholder must be an exact variable name. +\item There are no directives. You must do all display logic (if, for, etc) + in the calling routine. +\item There is, however, a ``block'' construct. A block is a portion of text + between the comment markers \code{<!-- BEGIN blockName --> \ldots + <!-- END blockName>}. The \code{set\_block} method extracts this text + into a namespace variable and puts a placeholder referring to it in the + template. This has a few parallels with Cheetah's \code{\#block} + directive but is overall quite different. +\item To do the equivalent of \code{\#if}, extract the block. Then if true, do + nothing. If false, assign the empty string to the namespace variable. +\item To do the equivalent of \code{\#for}, extract the block. Set any + namespace variables needed inside the loop. To parse one iteration, use + the \code{parse} method to fill the block variable (a mini-template) into + another namespace variable, appending to it. Refresh the namespace + variables needed inside the loop and parse again; repeat for each + iteration. You'll end up with a mini-result that will be plugged into the + main template's placeholder. +\item To read a template definition from a file, use the \code{set\_file} + method. This places the file's content in a namespace variable. + To read a template definition from a string, assign it to a namespace + variable. +\item Thus, for complicated templates, you are doing a lot of recursive block + filling and file reading and parsing mini-templates all into one flat + namespace as you finally build up values for the main template. In + Cheetah, all this display logic can be embedded into the template using + directives, calling out to Python methods for the more complicated tasks. +\item Although you can nest blocks in the template, it becomes tedious and + arguably hard to read, because all blocks have identical syntax. Unless + you choose your block names carefully and put comments around them, it's + hard to tell which blocks are if-blocks and which are for-blocks, or what + their nesting order is. +\item PHPLib templates do not have caching, output filters, etc. +\end{itemize} + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\subsection{Cheetah vs. PSP, PHP, ASP, JSP, Embperl, etc.} +\label{comparisons.pspEtc} + +\begin{description} +\item[Webware's PSP Component] -- \url{http://webware.sourceforge.net/Webware/PSP/Docs/} +\item[Tomcat JSP Information] -- \url{http://jakarta.apache.org/tomcat/index.html} +\item[ASP Information at ASP101] -- \url{http://www.asp101.com/} +\item[Embperl] -- \url{http://perl.apache.org/embperl/} +\end{description} + + +Here's a basic Cheetah example: +\begin{verbatim} +<TABLE> +#for $client in $service.clients +<TR> +<TD>$client.surname, $client.firstname</TD> +<TD><A HREF="mailto:$client.email" >$client.email</A></TD> +</TR> +#end for +</TABLE> +\end{verbatim} + +Compare this with PSP: + +\begin{verbatim} +<TABLE> +<% for client in service.clients(): %> +<TR> +<TD><%=client.surname()%>, <%=client.firstname()%></TD> +<TD><A HREF="mailto:<%=client.email()%>"><%=client.email()%></A></TD> +</TR> +<%end%> +</TABLE> +\end{verbatim} + +% Local Variables: +% TeX-master: "users_guide" +% End: |