Add QuerySet.map to manager class + type checking + tests + docs

docs/querysets.md

@@ -203,4 +203,18 @@ example of `order_by()`.
 >>> queryset.distinct('last_name')
 [Character(first_name='Robert', last_name='Baratheron'),
  Character(first_name='Catelyn', last_name='Stark')]
+```
+
+##### [](#header-5)map(func)
+
+Applies a `callable` function on each item in the `QuerySet` and yields
+a generator `map` object containing the result.
+
+**Example:**
+```py
+>>> queryset
+[Character(first_name='robert', last_name='baratheron'),
+ Character(first_name='catelyn', last_name='stark')]
+>>> list(queryset.map(lambda x: x.first_name.upper()))
+['ROBERT', 'CATELYN']
 ```

reobject/models/manager.py

@@ -171,6 +171,12 @@ def random(self) -> object:
         """
         return self.all().random()
 
+    def map(self, func) -> object:
+        """
+        Returns a random model instance.
+        """
+        return self.all().map(func)
+
     def __repr__(self):
         return '<{manager}: {model}>'.format(
             manager=type(self).__name__, model=self.model.__name__

reobject/query/queryset.py

@@ -137,8 +137,13 @@ def latest(self, field_name='created'):
         else:
             return obj
 
-    def map(self, callable):
-        return map(callable, self)
+    def map(self, func):
+        if not callable(func):
+            raise TypeError(
+                'Expected a callable, got {}'.format(type(func))
+            )
+
+        return map(func, self)
 
     def none(self):
         return EmptyQuerySet(model=self.model)

tests/unit/test_queryset.py

@@ -344,3 +344,13 @@ def test_manager_random(self):
         obj = SomeModel.objects.random()
 
         self.assertIn(obj, SomeModel.objects.all())
+
+    def test_manager_map(self):
+        SomeModel(p='foo', q=1)
+        SomeModel(p='bar', q=2)
+
+        result = SomeModel.objects.map(
+            func=lambda obj: obj.p.upper()
+        )
+
+        self.assertEqual(set(result), {'FOO', 'BAR'})