Django percentage field

I’m trying to create a percentage field in Django, where the user just fills in 40 for 40%. There will be a percentage sign on the right of the input box so that they know they should fill in a percentage. 0.4 must be stored in the DB. So far I’ve tried the following:

class PercentageField(fields.FloatField):
    widget = fields.TextInput(attrs={"class": "percentInput"})

    def to_python(self, value):
        val = super(PercentageField, self).to_python(value)
        if is_number(val):
            return val/100
        return val

    def prepare_value(self, value):
        val = super(PercentageField, self).prepare_value(value)
        if is_number(val):
            return str((float(val)*100))
        return val

def is_number(s):
    if s is None:
        return False
    try:
        float(s)
        return True
    except ValueError:
        return False

It works, but the problem is, when I post invalid data and the form is rendered again, it displays the 40 as 4000. In other words it multiplies the number again with 100 without dividing it as well.

Any suggestions how I can fix it?

I’ve tried this solution, but it repeats the value 100 times. It also has the same problem after I’ve corrected that.

I’m using Python3.5

Answer

I found the solution. I have to check whether the incoming value is a string. If it is, I don’t multiply by 100 since it came from the form. See below:

class PercentageField(fields.FloatField):
    widget = fields.TextInput(attrs={"class": "percentInput"})

    def to_python(self, value):
        val = super(PercentageField, self).to_python(value)
        if is_number(val):
            return val/100
        return val

    def prepare_value(self, value):
        val = super(PercentageField, self).prepare_value(value)
        if is_number(val) and not isinstance(val, str):
            return str((float(val)*100))
        return val