Bug #841

TemplateParser triggers TemplateKeyError if an "if" clause refers to a non-existing key, and no way to check if key exists before triggering if clause.

Added by Niek Bergman almost 12 years ago. Updated over 11 years ago.

Niek Bergman
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TemplateParser triggers a TemplateKeyError if an {{ if [var] }} clause is triggered when "var" is not defined. There is also no way currently to check if a variable is defined in a template and trigger a conditional block based on if the variable has been defined.

Associated revisions

Revision 246:98f9f7574ef5 (diff)
Added by Elmer de Looff almost 12 years ago

Corrected wrong error class raised. Tags that are not found should always raise TemplateNameError, not TemplateKeyError. This is related to issue #841.

Revision 248:52b0751e2acf (diff)
Added by Elmer de Looff almost 12 years ago

Introduced {{ ifpresent }} construct to TemplateParser. This checks for presence of the provided tags and their indices. Multiple tags can be provided per check, as well as {{ elif }} and {{ else }} clauses, where {{ elif }} supports additional tags. This resolves #841.


#1 Updated by Elmer de Looff almost 12 years ago

  • Status changed from New to Resolved
  • % Done changed from 0 to 70

Applied in changeset 52b0751e2acf.

#2 Updated by Elmer de Looff almost 12 years ago

  • Category set to TemplateParser
  • Assignee changed from Elmer de Looff to Niek Bergman
  • Target version set to µWeb alpha release


The TemplateKeyError you encountered should've been a TemplateNameError, which has been changed in r246. The {{ if }} construct does not and will not support referencing nonexistent template variables, because this would inevitably lead to disastrous surprises.

However, I've added a construct that does exactly what you want to do here, and that is checking the presence of a tag, or even its index:

  {{ ifpresent [one] [two]}}
    <p>key number <b>one</b> AND <b>two</b> are provided</p>
  {{ elif [three] }} 
    <p>one of keys <b>one</b> and <b>two</b> (or both) are missing, though <b>three</b> is provided</p>
  {{ else }}
    <p>none of the keys are provided</p>
  {{ endif }}

Please verify these changes work for you.

#3 Updated by Niek Bergman almost 12 years ago

Confirmed to work.

#4 Updated by Elmer de Looff over 11 years ago

  • Status changed from Resolved to Closed
  • % Done changed from 70 to 100

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