How to write code that works in both Python 2 and Python 3?

Question

A Django website I maintain currently uses Python 2.7 but I know that I\'ll have to upgrade it to Python 3 in a couple of months. If I\'m writing code right now that has to

Answer 1

Making your Django project compatible with both Python versions consists of the following steps:

1. Add from __future__ import unicode_literals at the top of each module and then use usual quotes without a u prefix for Unicode strings and a b prefix for bytestrings.

2. To ensure that a value is bytestring, use the django.utils.encoding.smart_bytes function. To ensure that a value is Unicode, use the django.utils.encoding.smart_text or django.utils.encoding.force_text function.

3. In your models use __str__ method instead of __unicode__ and add the python_2_unicode_compatible decorator.

   # models.py
   # -*- coding: UTF-8 -*-
   from __future__ import unicode_literals
   from django.db import models
   from django.utils.translation import ugettext_lazy as _
   from django.utils.encoding import python_2_unicode_compatible
   
   @python_2_unicode_compatible
   class NewsArticle(models.Model):
       title = models.CharField(_("Title"), max_length=200)
        content = models.TextField(_("Content"))
   
       def __str__(self):
           return self.title
   
       class Meta:
           verbose_name = _("News Article")
           verbose_name_plural = _("News Articles")
   

4. To iterate through dictionaries, use iteritems() , iterkeys() , and itervalues() from django.utils.six . Take a look at the following:

   from django.utils.six import iteritems
   
   d = {"imported": 25, "skipped": 12, "deleted": 3}
   for k, v in iteritems(d):
       print("{0}: {1}".format(k, v))
   

5. At the time of capturing exceptions, use the as keyword, as follows:

   try:
       article = NewsArticle.objects.get(slug="hello-world")
   except NewsArticle.DoesNotExist as exc:
       pass
   except NewsArticle.MultipleObjectsReturned as exc:
       pass
   

6. Use django.utils.six to check the type of a value as shown in the following:

   from django.utils import six
   
   isinstance(val, six.string_types) # previously basestring
   isinstance(val, six.text_type) # previously unicode
   isinstance(val, bytes) # previously str
   isinstance(val, six.integer_types) # previously (int, long)
   

7. Use range from django.utils.six.moves ,Instead of xrange , as follows:

   from django.utils.six.moves import range
   
   for i in range(1, 11):
      print(i)
   

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