[model-bakers#93] Add support for suffix in seq

- This adds a new `suffix` keyword arg to the `seq` function to allow
  the concatenation of a common suffix string onto a generated `seq`
  value.
- This adds a section under "Sequences in recipes" to the documentation
  to provide example usage of the new keyword argument.
  - Additionally, an `email` field is added to the `Customer` example
    model in the README.md to go along with the new section in the
    documentation.
- This also adds unit tests for the new keyword argument behavior.

README.md

@@ -28,6 +28,7 @@ pip install model_bakery
 class Customer(models.Model):
     enjoy_jards_macale = models.BooleanField()
     name = models.CharField(max_length=30)
+    email = models.CharField(max_length=50)
     age = models.IntegerField()
     bio = models.TextField()
     days_since_last_login = models.BigIntegerField()

docs/source/recipes.rst

@@ -225,6 +225,24 @@ Sometimes, you have a field with an unique value and using ``make`` can cause ra
 
 This will append a counter to strings to avoid uniqueness problems and it will sum the counter with numerical values.
 
+An optional ``suffix`` parameter can be supplied to augment the value for cases like generating emails
+or other strings with common suffixes.
+
+.. code-block:: python
+
+    >>> from model_bakery import.recipe import Recipe, seq
+    >>> from shop.models import Customer
+
+    >>> customer = Recipe(Customer, email=seq('user', suffix='@example.com'))
+
+    >>> customer = baker.make_recipe('shop.customer')
+    >>> customer.email
+    'user1@example.com'
+
+    >>> customer = baker.make_recipe('shop.customer')
+    >>> customer.email
+    'user2@example.com'
+
 Sequences and iterables can be used not only for recipes, but with ``baker`` as well:
 
 .. code-block:: python

model_bakery/utils.py

@@ -20,7 +20,7 @@ def import_from_str(import_string):
         return import_string
 
 
-def seq(value, increment_by=1, start=None):
+def seq(value, increment_by=1, start=None, suffix=None):
     if type(value) in [datetime.datetime, datetime.date, datetime.time]:
         if start:
             msg = "start parameter is ignored when using seq with date, time or datetime objects"
@@ -46,4 +46,4 @@ def seq(value, increment_by=1, start=None):
                 yield series_date
     else:
         for n in itertools.count(start or increment_by, increment_by):
-            yield value + type(value)(n)
+            yield value + type(value)(n) + (suffix or type(value)())

tests/test_recipes.py

@@ -413,6 +413,17 @@ def test_increment_for_strings(self):
         person = baker.make_recipe("tests.generic.serial_person")
         assert person.name == "joe3"
 
+    def test_increment_for_strings_with_suffix(self):
+        from model_bakery.recipe import seq  # NoQA
+
+        fred_person = person_recipe.extend(name=seq("fred", suffix="@example.com"))
+        person = fred_person.make()
+        assert person.name == "fred1@example.com"
+        person = fred_person.make()
+        assert person.name == "fred2@example.com"
+        person = fred_person.make()
+        assert person.name == "fred3@example.com"
+
     def test_increment_for_numbers(self):
         dummy = baker.make_recipe("tests.generic.serial_numbers")
         assert dummy.default_int_field == 11
@@ -442,6 +453,20 @@ def test_increment_for_numbers_2(self):
         assert dummy.default_decimal_field == Decimal("23.1")
         assert dummy.default_float_field == 4.23
 
+    def test_increment_for_numbers_with_suffix(self):
+        from model_bakery.recipe import seq  # NoQA
+
+        dummy = baker.make_recipe(
+            "tests.generic.serial_numbers", default_int_field=seq(1, suffix=1)
+        )
+        assert dummy.default_int_field == 3
+
+        with pytest.raises(TypeError):
+            dummy = baker.make_recipe(
+                "tests.generic.serial_numbers",
+                default_int_field=seq(1, suffix="this should fail"),
+            )
+
     def test_creates_unique_field_recipe_using_for_iterator(self):
         for i in range(1, 4):
             dummy = baker.make_recipe("tests.generic.dummy_unique_field")