Fixed #21951 -- Updated docs to use __str__ for Python 3

Thanks Tim Graham for the report and recommendations

docs/topics/db/examples/many_to_many.txt

@@ -16,8 +16,7 @@ objects, and a ``Publication`` has multiple ``Article`` objects:
     class Publication(models.Model):
         title = models.CharField(max_length=30)
 
-        # On Python 3: def __str__(self):
-        def __unicode__(self):
+        def __str__(self):              # __unicode__ on Python 2
             return self.title
 
         class Meta:
@@ -27,8 +26,7 @@ objects, and a ``Publication`` has multiple ``Article`` objects:
         headline = models.CharField(max_length=100)
         publications = models.ManyToManyField(Publication)
 
-        # On Python 3: def __str__(self):
-        def __unicode__(self):
+        def __str__(self):              # __unicode__ on Python 2
             return self.headline
 
         class Meta:

docs/topics/db/examples/many_to_one.txt

@@ -15,17 +15,15 @@ To define a many-to-one relationship, use :class:`~django.db.models.ForeignKey`.
         last_name = models.CharField(max_length=30)
         email = models.EmailField()
 
-        # On Python 3: def __str__(self):
-        def __unicode__(self):
-            return u"%s %s" % (self.first_name, self.last_name)
+        def __str__(self):              # __unicode__ on Python 2
+            return "%s %s" % (self.first_name, self.last_name)
 
     class Article(models.Model):
         headline = models.CharField(max_length=100)
         pub_date = models.DateField()
         reporter = models.ForeignKey(Reporter)
 
-        # On Python 3: def __str__(self):
-        def __unicode__(self):
+        def __str__(self):              # __unicode__ on Python 2
             return self.headline
 
         class Meta:

docs/topics/db/examples/one_to_one.txt

@@ -16,26 +16,23 @@ In this example, a ``Place`` optionally can be a ``Restaurant``:
         name = models.CharField(max_length=50)
         address = models.CharField(max_length=80)
 
-        # On Python 3: def __str__(self):
-        def __unicode__(self):
-            return u"%s the place" % self.name
+        def __str__(self):              # __unicode__ on Python 2
+            return "%s the place" % self.name
 
     class Restaurant(models.Model):
         place = models.OneToOneField(Place, primary_key=True)
         serves_hot_dogs = models.BooleanField()
         serves_pizza = models.BooleanField()
 
-        # On Python 3: def __str__(self):
-        def __unicode__(self):
-            return u"%s the restaurant" % self.place.name
+        def __str__(self):              # __unicode__ on Python 2
+            return "%s the restaurant" % self.place.name
 
     class Waiter(models.Model):
         restaurant = models.ForeignKey(Restaurant)
         name = models.CharField(max_length=50)
 
-        # On Python 3: def __str__(self):
-        def __unicode__(self):
-            return u"%s the waiter at %s" % (self.name, self.restaurant)
+        def __str__(self):              # __unicode__ on Python 2
+            return "%s the waiter at %s" % (self.name, self.restaurant)
 
 What follows are examples of operations that can be performed using the Python
 API facilities.