Question

We use django admin as a client-facing backend, so we need to make it user friendly. I have a model with a bunch of DecimalFields representing nutritional data.

The fields all look like this:

g_carbs = DecimalField(max_digits=13, decimal_places = 8, null=True, blank=True)

If the field is left blank, or if a non-zero value is provided, the admin form looks and works great. For example, for a non-blank, non-zero value like 10.5, it displays something like 10.50000000, which is fine.

The problem is that for any 0 values, the form field displays 0E-8 which, although technically correct, is not going to cut it for my clients, who are definitely not scientists or engineers for the most part and are unfamiliar with E notation.

I am not using a custom form or any custom admin tricks. Its just what gets auto-rendered by django admin for that model. I’m considering submitting a ticket to django for this, but in the mean time is there something I can do with a custom form or something to remedy this problem?

Answer 1

Here’s what ended up working for me (so far). This both prevents E notation and removes trailing 0’s after the decimal point.

class NonscientificDecimalField(DecimalField):
    """ Prevents values from being displayed with E notation, with trailing 0's 
        after the decimal place  truncated. (This causes precision to be lost in 
        many cases, but is more user friendly and consistent for non-scientist 
        users)
    """
    def value_from_object(self, obj):
        def remove_exponent(val):
            """Remove exponent and trailing zeros.
               >>> remove_exponent(Decimal('5E+3'))
               Decimal('5000')
            """
            context = decimal.Context(prec=self.max_digits)
            return val.quantize(decimal.Decimal(1), context=context) if val == val.to_integral() else val.normalize(context)

        val = super(NonscientificDecimalField, self).value_from_object(obj)
        if isinstance(val, decimal.Decimal):
            return remove_exponent(val)