Django templates: If false?

Django Problem Overview

How do I check if a variable is False using Django template syntax?

{% if myvar == False %}

Doesn't seem to work.

Note that I very specifically want to check if it has the Python value False. This variable could be an empty array too, which is not what I want to check for.

Django Solutions

Solution 1 - Django

For posterity, I have a few NullBooleanFields and here's what I do:

To check if it's True:

{% if variable %}True{% endif %}

To check if it's False (note this works because there's only 3 values -- True/False/None):

{% if variable != None %}False{% endif %}

To check if it's None:

{% if variable == None %}None{% endif %}

I'm not sure why, but I can't do variable == False, but I can do variable == None.

Solution 2 - Django

Django 1.10 (release notes) added the is and is not comparison operators to the if tag. This change makes identity testing in a template pretty straightforward.

In[2]: from django.template import Context, Template

In[3]: context = Context({"somevar": False, "zero": 0})

In[4]: compare_false = Template("{% if somevar is False %}is false{% endif %}")
In[5]: compare_false.render(context)
Out[5]: u'is false'

In[6]: compare_zero = Template("{% if zero is not False %}not false{% endif %}")
In[7]: compare_zero.render(context)
Out[7]: u'not false'

If You are using an older Django then as of version 1.5 (release notes) the template engine interprets True, False and None as the corresponding Python objects.

In[2]: from django.template import Context, Template

In[3]: context = Context({"is_true": True, "is_false": False, 
                          "is_none": None, "zero": 0})

In[4]: compare_true = Template("{% if is_true == True %}true{% endif %}")
In[5]: compare_true.render(context)
Out[5]: u'true'

In[6]: compare_false = Template("{% if is_false == False %}false{% endif %}")
In[7]: compare_false.render(context)
Out[7]: u'false'

In[8]: compare_none = Template("{% if is_none == None %}none{% endif %}")
In[9]: compare_none.render(context)
Out[9]: u'none'

Although it does not work the way one might expect.

In[10]: compare_zero = Template("{% if zero == False %}0 == False{% endif %}")
In[11]: compare_zero.render(context)
Out[11]: u'0 == False'

Solution 3 - Django

I think this will work for you:

{% if not myvar %}

Solution 4 - Django

You could write a custom template filter to do this in a half-dozen lines of code:

from django.template import Library

register = Library()

@register.filter
def is_false(arg): 
    return arg is False

Then in your template:

{% if myvar|is_false %}...{% endif %}

Of course, you could make that template tag much more generic... but this suits your needs specifically ;-)

Solution 5 - Django

In old version you can only use the ifequal or ifnotequal

{% ifequal YourVariable ExpectValue %}
    # Do something here.
{% endifequal %}

Example:

{% ifequal userid 1 %}
  Hello No.1
{% endifequal %}

{% ifnotequal username 'django' %}
  You are not django!
{% else %}
  Hi django!
{% endifnotequal %}

As in the if tag, an {% else %} clause is optional.

The arguments can be hard-coded strings, so the following is valid:

{% ifequal user.username "adrian" %} ... {% endifequal %} An alternative to the ifequal tag is to use the if tag and the == operator.

ifnotequal Just like ifequal, except it tests that the two arguments are not equal.

An alternative to the ifnotequal tag is to use the if tag and the != operator.

However, now we can use if/else easily

{% if somevar >= 1 %}
{% endif %}

{% if "bc" in "abcdef" %}
  This appears since "bc" is a substring of "abcdef"
{% endif %}

Complex expressions

All of the above can be combined to form complex expressions. For such expressions, it can be important to know how the operators are grouped when the expression is evaluated - that is, the precedence rules. The precedence of the operators, from lowest to highest, is as follows:

or
and
not
in
==, !=, <, >, <=, >=

More detail

https://docs.djangoproject.com/en/dev/ref/templates/builtins/

Solution 6 - Django

Just ran into this again (certain I had before and came up with a less-than-satisfying solution).

For a tri-state boolean semantic (for example, using models.NullBooleanField), this works well:

{% if test.passed|lower == 'false' %} ... {% endif %}

Or if you prefer getting excited over the whole thing...

{% if test.passed|upper == 'FALSE' %} ... {% endif %}

Either way, this handles the special condition where you don't care about the None (evaluating to False in the if block) or True case.

Solution 7 - Django

I have had this issue before, which I solved by nested if statements first checking for none type separately.

{% if object.some_bool == None %}Empty
{% else %}{% if not object.some_bool %}False{% else %}True{% endif %}{% endif %}

If you only want to test if its false, then just

{% if some_bool == None %}{% else %}{% if not some_bool %}False{% endif %}{% endif %}

EDIT: This seems to work.

{% if 0 == a|length %}Zero-length array{% else %}{% if a == None %}None type{% else %}{% if not a %}False type{% else %}True-type {% endif %}{% endif %}{% endif %}

Now zero-length arrays are recognized as such; None types as None types; falses as False; Trues as trues; strings/arrays above length 0 as true.

You could also include in the Context a variable false_list = [False,] and then do

{% if some_bool in false_list %}False {% endif %}

Solution 8 - Django

Look at the yesno helper

Eg:

{{ myValue|yesno:"itwasTrue,itWasFalse,itWasNone" }}

Solution 9 - Django

I've just come up with the following which is looking good in Django 1.8

Try this instead of value is not False:

if value|stringformat:'r' != 'False'

Try this instead of value is True:

if value|stringformat:'r' == 'True'

unless you've been really messing with repr methods to make value look like a boolean I reckon this should give you a firm enough assurance that value is True or False.

Solution 10 - Django

This is far easier to check in Python (i.e. your view code) than in the template, because the Python code is simply:

myvar is False

Illustrating:

>>> False is False
True
>>> None is False
False
>>> [] is False
False

The problem at the template level is that the template if doesn't parse is (though it does parse in). Also, if you don't mind it, you could try to patch support for is into the template engine; base it on the code for ==.

Solution 11 - Django

you can use the int value of true and false

True = any int False = zero so, if we take an example:

{% if user.is_authenticated == 1 %}
do something
{% endif %}

this mean in python

if user.is_authenticated:
    #do something

and

{% if user.is_authenticated == 0 %}
do something
{% endif %}