Transcript Python template engines and implementation in Indico

Python template engines and
implementation in Indico
Marius Damarackas (Vilnius University)
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About me
• Software engineering student
• Doing 3 months long internship in CERN
• Improving Indico template system
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Outline
1. History of Indico templates
2. Why change the current system?
3. Main tasks
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Research about available template systems
Integration of the new engine
Replacing XSLT with normal templates
4. Remaining work
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History of Indico templates
• First generation
>>> '<div width="100%%">%(param)s</div>' % {'param' : 'Value'}
'<div width="100%>Value</div>'
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History of Indico templates
• Second generation
<% import some.module %>
<% foobarList = some.module.createList() %>
<table>
<% for foo in foobarList: %>
<tr>
<% if foo == bar: %>
<td><%= foo %></td>
<% end %>
<% else: %>
<td>foobar</td>
<% end %>
</tr>
<% end %>
</table>
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Why change the current system?
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Maintenance costs
Slow when including other templates
No cache
No HTML escaping
Strange usage of the colon symbols:
<% latestNews = newsList[:5] %>
<% end %>
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1. Research
• Some of the candidates
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Genshi
Mako
Cheetah
Jinja2
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1. Research
• Genshi
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Claims to be the fastest XML template engine
Used by Trac
XML and Text versions
Features like caching, XSS protections
▫ Slow
▫ Very difficult to translate Indico templates
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1. Research
• Mako
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Used by python.org and reddit.com
Very fast: compiles to Python modules
Allows to disable Unicode (a plus for Indico)
Template inheritance mechanism
▫ Syntax could be better, more unified
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1. Research
• Jinja2
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Quite fast
Template inheritance
Strong separation of logic and presentation
Difficult to adapt to Indico
• Cheetah
▫ Manual compilation to Python modules
 Mako does it automatically
▫ Personally I did not like the syntax
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2. Integration
• Replace old engine code with TemplateLookup
• Problem: more than 800 .tpl files to translate
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2. Integration
• Using a script to convert files
• Mainly based on regexps
• Some things needed to be changed by hand
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2. Testing integration
• Basic idea to test the integration:
▫ use *both* old Indico and new Mako templates
• Generate outputs and do diff
• If there are significant differences, save them
• Analyze differences and fix the script
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2. Testing integration
• Coverage: 450+ out of 800 templates
• 56%, but higher if we count only active files
• Allowed to catch some bugs in the script
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3. Replacing XSLT
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3. Replacing XSLT
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Generates XML, then applies transformations
Slow
Different from other parts of the system
Lots of code duplication
Difficult to maintain
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3. Replacing XSLT
• Maintenance problems
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if (chatInfoState]]></xsl:text>
<xsl:value-of select="./id" disable-output-escaping="yes"/>
<xsl:text disable-output-escaping="yes"><![CDATA[) {
IndicoUI.Effect.slide('collaborationInfoLine]]></xsl:text>
<xsl:value-of select="./id" disable-output-escaping="yes"/>
<xsl:text disable-output-escaping="yes"><![CDATA[', height]]></xsl:text>
<xsl:value-of select="./id" disable-output-escaping="yes"/>
<xsl:text disable-output-escaping="yes"><![CDATA[);
$E('CRMoreInfo]]></xsl:text>
<xsl:value-of select="./id" disable-output-escaping="yes"/>
<xsl:text disable-output-escaping="yes"><![CDATA[').set('More info');
$E('CRMoreInfo]]></xsl:text>
<xsl:value-of select="./id" disable-output-escaping="yes"/>
<xsl:text disable-output-escaping="yes">
<![CDATA[').dom.className = "CRDisplayMoreInfo";
…
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3. Replacing XSLT
• Same code in human language
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if (chatInfoState${id}) {
IndicoUI.Effect.slide('collaborationInfoLine${id}', height${id});
$E('CRMoreInfo${id}').set('More info');
$E('CRMoreInfo${id}').dom.className = "CRDisplayMoreInfo";
…
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3. Replacing XSLT
• Performance:
▫ Changing the way parameters are passed
▫ No XML
• Maintenance:
▫ Most of the styles are similar
▫ Using Mako template inheritance
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Remaining work
• Think of a smart way to restructure event styles
• Fix the i18n script to support the new syntax
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Thank you