django-expression-fields 0.1.1

django-expression-fields allows typing mathematical expressions into form fields and having only the calculated result stored in the database.

Introduction

django-expression-fields lets your users type a mathematical expression in a form field. Python does the math and stores the result in the database. For example, suppose you have a model to track Things, like this:

class Thing(models.Model):

cost = models.DecimalField(

max_digits=5, decimal_places=2, null=True, blank=True)

Suppose Things come in packs of 12 for $7.99. Your users have to do some math to fill in the cost of a single Thing, $0.67.

But not with an expression field! Create your form like this:

class ThingForm(forms.Form):

cost = DecimalExpressionField(

max_digits=5, decimal_places=2, required=False)

Now you user can simply type 7.99/12 in the field and Python will do the math for them!

Requirements and Installation

Right now, the project has no dependencies.

• pip install django-expression-fields

• Add expression_fields to your INSTALLED_APPS.

Use

from django import forms from expression_fields.fields import DivideDecimalField

class MyForm(forms.Form):

cost = DecimalExpressionField(

max_digits=5, decimal_places=2, required=False)

Tests

./run-tests.sh.

Limitations

Right now there is only the DivideDecimalField which allows a single division sign. It’s a proof of concept for a fuller DecimalExpression field which will allow full expressions. I later intend to build Integer and Float expression fields as well.

Contributions

I built this little project to satisfy a personal need, but thought it might be useful enough for others. If you have contributions, please don’t hesitate to send a PR. Let’s keep the tests passing and all will be well. My personal stack is currently Django 1.8 on Python 3.4, but once I can get some Travis set up, there’s no reason not to support other versions.