In Jinja2 how do you test if a variable is undefined

Question

Converting from Django  I m used to doing something like this      if not var1       endif      and having it work if I didn t put var1 into the context  Jinja2 gives me an undefined error  Is there an easy way to say    if var1    None    or similar

User · Accepted Answer

From the Jinja2 template designer documentation      if variable is defined        value of variable     variable       else        variable is not defined    endif

User · Answer

Consider using default filter if it is what you need  For example      set host   jabber host   default default host  -     or use more fallback values with  hardcoded  one at the end like      set connectTimeout   config stackowerflow connect timeout   default config stackowerflow timeout    default config timeout    default 42  -

User · Answer

if variable is defined    works to check if something is undefined   You can get away with using    if not var1    if you default your variables to False eg   class MainHandler BaseHandler       def get self           var1   self request get  var1   False

User · Answer

You could also define a variable in a jinja2 template like this      if step is not defined       set step   1       endif      And then You can use it like this      if step    1     lt div class  col-xs-3 bs-wizard-step active  gt     elif step  gt  1     lt div class  col-xs-3 bs-wizard-step complete  gt     else     lt div class  col-xs-3 bs-wizard-step disabled  gt     endif      Otherwise  if You wouldn t use    set step   1     the upper code would throw   UndefinedError   step  is undefined

User · Answer

if variable is defined    is true if the variable is  None   Since not is None is not allowed  that means that     if variable    None     is really your only option

User · Answer

In the Environment setup  we had undefined   StrictUndefined  which prevented undefined values from being set to anything  This fixed it   from jinja2 import Undefined JINJA2 ENVIRONMENT OPTIONS      undefined    Undefined

[jinja2] In Jinja2, how do you test if a variable is undefined?

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