Handling an undefined template variable in Tornado

python, tornado

Solution

Hacking around using `locals().get()` is one way to do it. Another, bit more orthodox is using `try`. Tornado template supports it, so you can:

{% try %}
  {% if logout_error %}
    Oops! The logout failed. Please close all open documents and try again
  {% end %}
{% except %}
{% end %}

Problem

This is a tornado template (say, in the file logout.html) I render on an error in the logout process: ``` {% if logout_error %} Oops! The logout failed. Please close all open documents and try again {% end %} ``` This can be called using ``` self.render("logout.html", logout_error=True) ``` If the logout is successful, I have to do ``` self.render("logout.html", logout_error=False) ``` If I ignore `logout_error=False`, I get ``` NameError: global name 'logout_error' is not defined ``` If there are a lot of flags (which are false), the keyword arguments can pile up. Is there a way I can ask the template to consider `logout_error` as `False` if it does not exist?

Original source

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