This blog is now hosted at

Friday, February 26, 2010

Numeric Formatting in Django

You might have seen my previous post lamenting the weirdnesses around number formatting in python.  This spills over into Django; if you have DecimalFields in your models (especially if you are using the ModelForm object to create your forms.

The previous "format Decimal object as a string that any 10-year-old would expect" method is:

def dec_string(dec):
    if isinstance(dec, Decimal):
        if dec:
            if dec.normalize().as_tuple().exponent > 0:
                return "%d"%dec
                return "%s"%dec.normalize()
            return 0
        return dec
(I added the isinstance() bit to protect me from myself =)

Since we know how to format this, all that remains to be done is to create a widget that automatically formats DecimalFields correctly.

class DecimalInput(TextInput):
  def render(self, name, value, attrs=None):
    value = dec_string(value)
    return super(DecimalInput, self).render(name, value, attrs)
And then just use that in your form:

class EnergyForm(ModelForm):
    kwh = DecimalField(widget=DecimalInput(attrs={'size':'6'}))

There is more to the ModelForm, but that's what the docs are for, right?

No comments: