testing for empty/null string in django

Question

I have a charfield with the following:

myString = models.CharField(max_length=50,null=True,blank=True)

In many of my objects, this particular string is often left blank, when created through the django admin interface. In MySQL, the column is VARCHAR(50) with default=NULL.

Whatever test I try to do in my views.py to detect blank values, always seems to evaluate to false whether the entry is blank or not:

myString is None
myString==""
len(myString)==0

How can I discriminate between blank and non-blank values for this field?

Thanks

EDIT:

Actual view is the following, I want to execute a block only if this field is not blank.

if myObject.myString:
     #do something

the block always executes, and I have tried all the above examples of testing for a blank field.

EDIT 2:

Scratch that, if myObject.myString: does indeed work.

myString is not a string -- it's a models.CharField. Show us your actual view where you're trying to do this. — agf
– agf, Commented Aug 9, 2011 at 11:12
so what does print myString or the equivalent show right before that if statement? You need to give us more info. — agf
– agf, Commented Aug 9, 2011 at 11:46
turns out the above does work, but needed to restart apache to get the altered code to execute. Oops. — meepmeep
– meepmeep, Commented Aug 9, 2011 at 12:02

Srikar Appalaraju · Accepted Answer · 2016-05-28 08:18:03Z

19

if your d is either None or "" then simply check -

if d: 
    #do something
else:
    #do something else

edited May 28, 2016 at 8:18

answered Aug 9, 2011 at 11:04

Srikar Appalaraju

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Heston Liebowitz · Accepted Answer · 2013-03-06 00:21:27Z

13

Some empty fields return empty strings while others return None. A nullable boolean field however, will return False when it has been set. This will not pass the test in Srikar's answer. A more robust solution is this:

if d in [None, '']:
    # This field is empty.

answered Mar 6, 2013 at 0:21

Heston Liebowitz

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Comments

agf · Accepted Answer · 2011-08-09 11:24:58Z

3

myString is not a string -- it's a models.CharField. Show us your actual view where you're trying to do this.

If you've already got an instance of your model, you should just be able to do

if model_instance.myString:

to test if it's not blank.

answered Aug 9, 2011 at 11:24

agf

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Comments

thisshri · Accepted Answer · 2019-05-06 12:51:33Z

1

In the case where your variable is either None or '' (blank), you can just handle both of the conditions as follows

if my_string:
  # neither None nor blank

answered May 6, 2019 at 12:51

thisshri

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