Django VersionNumberField

version_number.py

import struct
from django.db import models
from south.modelsinspector import add_introspection_rules
add_introspection_rules([], ["^core\.fields\.version_number\.VersionNumberField"])

class VersionNumber(object):
    def __init__(self, major, minor=0, patch=0, build=0):
        self.number = (int(major), int(minor), int(patch), int(build))

    def __str__(self):
        """
        Pretty printing of version number; doesn't print 0's on the end
        """
        end_index = 0
        for index, part in enumerate(self.number):
            if part != 0:
                end_index = index

        return ".".join([str(i) for i in self.number[:end_index+1]])

class VersionNumberField(models.Field):
    """
    A version number. Stored as a integer. Retrieved as a VersionNumber. Like
    magic. Major, minor, patch, build must not exceed 255
    """
    __metaclass__ = models.SubfieldBase

    def get_internal_type(self):
        return 'IntegerField'

    def to_python(self, value):
        """
        Convert a int to a VersionNumber
        """
        if value is None:
            return None
        if isinstance(value, VersionNumber):
            return value
        if isinstance(value, tuple):
            return VersionNumber(*value)

        part_bytes = struct.pack(">I", value)
        part_ints = [ord(i) for i in part_bytes]
        return VersionNumber(*part_ints)

    def get_prep_value(self, value):
        """
        Convert a VersionNumber or tuple to an int
        """
        if isinstance(value, tuple):
            value = VersionNumber(*value)
        if isinstance(value, int):
            return value

        major, minor, patch, build = value.number
        return major << 24 | minor << 16 | patch << 8 | build

    def value_to_string(self, obj):
        value = self._get_value_from_obj(obj)
        return self.get_db_prep_value(value)