Python template engines and implementation in IndicoMarius 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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Outline1. History of Indico templates2. Why change the current system?3. Main tasks• 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?•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

▫Genshi▫Mako▫Cheetah▫Jinja2

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1. Research•Genshi

▫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

▫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

▫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•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…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…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