Twiddler

  Simply twiddling stuff from the outside!

  Twiddler seeks to provide a way to render textual content from
  template sources. It has two main aims:

  - be able to work with source material provided by designers and
    leaving them absolutely unchanged or work absolutely seamlessly
    with visual editors if there is any markup that needs to be
    added.

  - be absolutely as simple as possible while still being able to
    handle all that needs to be done. This, in particular, means no
    new languages should need to be known to be use Twiddler!

  Before You Start

    You will need to know the syntax of the content you wish to
    generate, be that XML, HTML or plain text.

    You will need to know some Python. You'll need to know very little
    to get going, but if you want to do more advanced manipulation,
    you'll need to know more.

  Installation

    The easyiest way to install Twiddler is:

      easy_install twiddler

    Or, if you're using zc.buildout, just specify 'twiddler' as 
    a required egg.

    However, you can also install by unpacking the source
    distribution and placing the 'twiddler' folder somewhere on your 
    PYTHONPATH.

    If you do not install using easy_install or zc.buildout, you will 
    also need to make sure the following python packages are available 
    on your PYTHONPATH:

    - elementtree
   
      Even though this comes as standard in Python 2.5 or above,
      Twiddler has not yet been made compatible with the version that
      ships with Python 2.5. ElementTree must be seperately installed
      no matter what version of Python you are using and it can be
      downloaded from:

      http://effbot.org/zone/element-index.htm
    
    - zope.interface

      This comes as standard in Zope 2.9.0 and above, but if you're
      not using Zope, you'll need to download it from:

      http://download.zope.org/distribution/

      You'll need a knowledge of python eggs although the INSTALL.TXT
      in the .tar.gz file gives instructions.

    - zope.testing

      This is only needed if you want to run the included unit and doc
      tests. It comes as standard in Zope 2.9.0 and above, but if
      you're not using Zope and want to run the tests, it can be
      seperately downloaded from:

      http://download.zope.org/distribution/

      You'll need a knowledge of python eggs although the INSTALL.TXT
      in the .tar.gz file gives instructions.

    For instructions on installation with the various python web
    frameworks, please see the "Further Information" section below.

  Usage

    To explain how Twiddlers work, we're going to use the plain python
    version of Twiddler and do everything from scratch. Once you've
    installed Twiddler for plain python, the following examples will
    all work just fine.

    So, to start off with, you create a Twiddler from some source
    string:
 
    >>> from twiddler import Twiddler
    >>> t = Twiddler('''<html>
    ...   <body>
    ...   <div id="greeting">Hello world!</div>
    ...   <div name="stuff">I'm in <i>Italic</i>!</div>
    ...   <form><input name="test" value="value"/></form>
    ...   </body>
    ... </html>''')

    From then on, you make the content dynamic by finding an element
    and then either replacing parts of it, removing it or repeating
    it. This can be done as often as you like. At any point, you can
    call the Twiddler's render method to get a string that you can
    return to the browser.

    Here's a couple of simple examples of replacement:

    >>> t['greeting'].replace('Hello user!',style='color: red;')
    >>> t['test'].replace(value='my value')

    We can see the results by rendering the Twiddler:

    >>> print t.render()
    <html>
      <body>
      <div id="greeting" style="color: red;">Hello user!</div>
      <div name="stuff">I'm in <i>Italic</i>!</div>
      <form><input name="test" value="my value" /></form>
      </body>
    </html>

    Here's a simple example of removal:

    >>> t['stuff'].remove()
    >>> print t.render()
    <html>
      <body>
      <div id="greeting" style="color: red;">Hello user!</div>
      <form><input name="test" value="my value" /></form>
      </body>
    </html>

    Here's a simple example of repeating:
    
    >>> e = t['greeting'].repeater()
    >>> for i in range(3):
    ...   e.repeat('Hello user %i!'%i,id='greeting'+str(i))    
    <twiddler.TwiddlerElement instance at ...>
    <twiddler.TwiddlerElement instance at ...>
    <twiddler.TwiddlerElement instance at ...>

    >>> print t.render()
    <html>
      <body>
      <div id="greeting0" style="color: red;">Hello user 0!</div>
      <div id="greeting1" style="color: red;">Hello user 1!</div>
      <div id="greeting2" style="color: red;">Hello user 2!</div>
      <form><input name="test" value="my value" /></form>
      </body>
    </html>

    You may be wondering where the <twiddler.twiddler...> lines in the
    output above are coming from. Well, they're an artifact of how the
    python shell behaves, but one caused by another feature.

    The repeat method returns the element that has just been
    inserted. This is useful if you want to repeat more complex
    structures:

    >>> t = Twiddler('''<html>
    ...   <body>
    ...   <div name="row">This is row <i name="number">1</i></div>
    ...   </body>
    ... </html>''')
    >>> e = t['row'].repeater()
    >>> for i in range(3):
    ...    c = e.repeat()
    ...    c['number'].replace(str(i),name=False)
    >>> print t.render()
    <html>
      <body>
      <div name="row">This is row <i>0</i></div>
      <div name="row">This is row <i>1</i></div>
      <div name="row">This is row <i>2</i></div>
      </body>
    </html>
    
    Now, you may have noticed that, so far, we've done all
    manipulation of the elements from code outside of the source
    code. Some people find the duality of source and code that
    manipulates the source, particularly when they're likely to be in
    different files on disk, unpleasant. To make life happier for
    these people, Twiddler supports the inclusion of a code block in
    the source itself as follows:

    >>> from twiddler.input.default import DefaultWithCodeBlock
    >>> t = Twiddler('''<html>
    ... <!--twiddler 
    ... def myfunc(t):
    ...   e = t['row'].repeater()
    ...   for i in range(3):
    ...     c = e.repeat()
    ...     c['number'].replace(str(i),name=False)
    ... -->
    ...   <body>
    ...   <div name="row">This is row <i name="number">1</i></div>
    ...   </body>
    ... </html>''',input=DefaultWithCodeBlock)

    This code is executed when the render method is called:

    >>> print t.render()
    <html>
      <body>
      <div name="row">This is row <i>0</i></div>
      <div name="row">This is row <i>1</i></div>
      <div name="row">This is row <i>2</i></div>
      </body>
    </html>

    You'll notice that to get this to work, a different input parser
    has to be specified. This is because code block execution can pose
    a significant security problem when the source of the Twiddler
    comes from user input and so the default parser that
    Twiddler uses will not look for code to execute.

    Now, when generating HTML, you often want to have a common style
    across many pages. Twiddler lets you do this by allowing you to
    insert parts of one Twiddler into another. 

    So, for example, here's our site template:

    >>> template = Twiddler('''<html>
    ...   <body>
    ...   <h1>The Site Header</h1>
    ...   <div id="content">Content goes here</div>
    ...   </body>
    ... </html>''')
    
    And here's a specific page:

    >>> page = Twiddler('''
    ... <html>
    ...   <body>
    ...   <div id="content">This is our page content!</div>
    ...   </body>
    ... </html>
    ... ''')
    
    Now, to put them together we do the following:

    >>> t = template.clone()
    >>> t['content'].replace(page['content'])
    >>> print t.render()
    <html>
      <body>
      <h1>The Site Header</h1>
      <div id="content">This is our page content!</div>
      </body>
    </html>

    Finally, at any point, Twiddler's can be pickled:

    >>> from cPickle import dumps,loads
    >>> s = dumps(t)

    This allows them to be saved to disk in a partially rendered
    state. This should provide some great opportunities for speeding
    up page rendering by only having to render the changes you need to
    make, when you need to make them.

    For example, the Twiddler we have just pickled could be reloaded,
    and just the content replaced, without having to be-build the page
    from the seperate page and template components:

    >>> from_cache = loads(s)
    >>> from_cache['content'].replace('Our new content!')
    >>> print from_cache.render()
    <html>
      <body>
      <h1>The Site Header</h1>
      <div id="content">Our new content!</div>
      </body>
    </html>

  Further Information

    More detailed information on each of Twiddler's aspects can be
    found in the 'docs' directory of the distribution:

      replace.txt - covers all possible uses of the replace method

      repeat.txt - covers all possible uses of the repeat method

      search.txt - covers all the ways you can search for elements

      filters.txt - the use of filters for spefic calls to replace and
                    repeat along with setting up default filters such
                    as html quoting and internationalisation.

      inandout.txt - covers the usage of Twiddler with different input parsers
                     and output renderers. This also covers the
                     default parse and render objects in more detail.

      execution.txt - covers all the ways that code can be executed as
                      a result of calling either the render of execute
                      methods. 

      templating.txt - covers the render, execute and clone methods as
                       used to build complete output from multiple
                       Twiddlers.

    In addition, the interfaces implemented by the various components
    that make up Twiddler are described in interfaces.py in the
    'twiddler' package.

    Instructions and examples for using Twiddler with various python
    web frameworks can also be found in the following files, contained
    within their sub-packages:

      zope2/readme.txt - covers usage of Twiddler in plain Zope 2.

  Licensing

     Copyright (c) 2006-2008 Simplistix Ltd

     This Software is released under the MIT License:
     http://www.opensource.org/licenses/mit-license.html
     See license.txt for more details.

  Credits

     Chris Withers - Idea and development

     Fredrik Lundh - The excellent ElementTree library

     The Django Guys - For the idea of filters

     Guido van Rossum - For being stubborn enough about XML that I thought more
                        deeply about parsing and rendering ;-)

  Changes

     0.9.0

       - changes to work with distutils, setuptools and zc.buildout

     0.8.0 

       - Initial Release
