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I'm trying to develop something using Django because it must be cross-platform. The easiest solution for cross-platform application is web-based application. Since I have just started and the document recommends me to use newforms instead of the oldforms. The concept of newforms is to define fields in the form for later validation and rendering the form in various formats and styles. However, the current implementation of newforms is in very early state (I guess) so there are so many missing pieces. For example, I would like to have a float field which automatically validates the input to be a valid floating point number. So I have to implement it myself.

Validating floating point number is very easy by just trying to float(value). However, it is not complete yet since sual limitations of a floating point number are max_digits and decimal_places. Django alreay provides a set of validators including IsValidFloat() so I will not write it again. Below is my FloatField.

from django.utils.translation import gettext
from django.core import validators
from django.newforms import Field
from django.newforms.util import ValidationError
 
__all__ = (
    'FloatField',
)
 
EMPTY_VALUES = (None, '')
 
class FloatField(Field):
    def __init__(self, max_digits=None, decimal_places=None, *args, **kwargs):
        self.max_digits, self.decimal_places = max_digits, decimal_places
        super(FloatField, self).__init__(*args, **kwargs)
 
    def clean(self, value):
        """
        Validates that float() can be called on the input. Returns the result
        of float(). Returns None for empty values.
        """
        super(FloatField, self).clean(value)
        if value in EMPTY_VALUES:
            return None
 
        try:
            value = float(value)
        except (ValueError, TypeError):
            raise ValidationError(gettext(u'Enter a float number.'))
        v = validators.IsValidFloat(self.max_digits, self.decimal_places)
        try:
            v(value, None)
        except validators.ValidationError, e:
            raise ValidationError(gettext(u'Enter a float number.'))
        return value

And then use FloatField as follows.

from django import newforms as forms
from django.newforms.widgets import HiddenInput
from mysite.myapp.forms import FloatField
 
class ItemForm(forms.Form):
    lineno = forms.IntegerField(widget=HiddenInput,required=False)
    product = forms.IntegerField(widget=HiddenInput)
    unit = forms.IntegerField(widget=HiddenInput)
    unit_price = forms.CharField(max_length=100,widget=HiddenInput)
    quantity = FloatField(max_digits=19,decimal_places=4)

Tags: django, newforms, codenone, floatfield