How to Check if request.GET var is None?


Question

I'm getting into django and this is getting me a headache. I'm trying to get a simple GET variable. URL is site.com/search/?q=search-term

My view is:

def search(request):
    if request.method == 'GET' and 'q' in request.GET:
        q = request.GET.get('q', None)
        if q is not None:
            results = Task.objects.filter(
                                   Q(title__contains=q)
                                   |
                                   Q(description__contains=q),
                                   )
            ...return...
        else:
            ...
    else:
        ...

Search queries like mysite.com/search/? (without q) get through the first if correctly.

The problem is in queries like mysite.com/search/?q=. They don't get caught by if q is not None:

So, the short answer would be How can I check q == None? (I've already tried '', None, etc, to no avail.)

1
24
2/27/2019 7:23:47 PM

Accepted Answer

First, check if the request.GET dict contains a parameter named q. You're doing this properly already:

if request.method == 'GET' and 'q' in request.GET:

Next, check if the value of q is either None or the empty string. To do that, you can write this:

q = request.GET['q']
if q is not None and q != '':
    # Do processing here

Notice that it is not necessary to write request.GET.get('q', None). We've already checked to make sure there is a 'q' key inside the request.GET dict, so we can grab the value directly. The only time you should use the get method is if you're not sure a dict has a certain key and want to avoid raising a KeyError exception.

However, there is an even better solution based on the following facts:

  • The value None evaluates to False
  • The empty string '' also evaluates to False
  • Any non-empty string evaluates to True.

So now you can write:

q = request.GET['q']
if q:
    # Do processing here

See these other resources for more details:

40
3/11/2010 3:59:43 AM

Thanks for the clarification by @Ned. Found a complete explanation here.

Basically:

'==' can be thought of as "value equality", that is, if two things look the same, == should return a true value. (For those with a Java background, Python's == is actually doing something akin to an equals() method.)

'is' can be thought of as 'object identity', that is, if the two things actually are the same object.


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