Merge pull request #1360 from lisongmin/add-default-value-to-groupby

Ability to set default value in groupby filter

4 files changed, 36 insertions, 3 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index dd3739f..c94894a 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -58,6 +58,8 @@ Unreleased
 -   ``NativeEnvironment`` supports async mode. :issue:`1362`
 -   Template rendering only treats ``\n``, ``\r\n`` and ``\r`` as line
     breaks. Other characters are left unchanged. :issue:`769, 952, 1313`
+-   ``|groupby`` filter takes an optional ``default`` argument.
+    :issue:`1359`
 
 
 Version 2.11.3
diff --git a/src/jinja2/asyncfilters.py b/src/jinja2/asyncfilters.py
index 11b031a..dfd8cba 100644
--- a/src/jinja2/asyncfilters.py
+++ b/src/jinja2/asyncfilters.py
@@ -107,8 +107,9 @@ async def do_groupby(
     environment: "Environment",
     value: "t.Union[t.AsyncIterable[V], t.Iterable[V]]",
     attribute: t.Union[str, int],
+    default: t.Optional[t.Any] = None,
 ) -> "t.List[t.Tuple[t.Any, t.List[V]]]":
-    expr = filters.make_attrgetter(environment, attribute)
+    expr = filters.make_attrgetter(environment, attribute, default=default)
     return [
         filters._GroupTuple(key, await auto_to_seq(values))
         for key, values in groupby(sorted(await auto_to_seq(value), key=expr), expr)
diff --git a/src/jinja2/filters.py b/src/jinja2/filters.py
index 33353e5..c925f83 100644
--- a/src/jinja2/filters.py
+++ b/src/jinja2/filters.py
@@ -1116,7 +1116,10 @@ class _GroupTuple(t.NamedTuple):
 
 @environmentfilter
 def do_groupby(
-    environment: "Environment", value: "t.Iterable[V]", attribute: t.Union[str, int]
+    environment: "Environment",
+    value: "t.Iterable[V]",
+    attribute: t.Union[str, int],
+    default: t.Optional[t.Any] = None,
 ) -> "t.List[t.Tuple[t.Any, t.List[V]]]":
     """Group a sequence of objects by an attribute using Python's
     :func:`itertools.groupby`. The attribute can use dot notation for
@@ -1148,10 +1151,22 @@ def do_groupby(
           <li>{{ group.grouper }}: {{ group.list|join(", ") }}
         {% endfor %}</ul>
 
+    You can specify a ``default`` value to use if an object in the list
+    does not have the given attribute.
+
+    .. sourcecode:: jinja
+
+        <ul>{% for city, items in users|groupby("city", default="NY") %}
+          <li>{{ city }}: {{ items|map(attribute="name")|join(", ") }}</li>
+        {% endfor %}</ul>
+
+    .. versionchanged:: 3.0
+        Added the ``default`` parameter.
+
     .. versionchanged:: 2.6
         The attribute supports dot notation for nested access.
     """
-    expr = make_attrgetter(environment, attribute)
+    expr = make_attrgetter(environment, attribute, default=default)
     return [
         _GroupTuple(key, list(values))
         for key, values in groupby(sorted(value, key=expr), expr)
diff --git a/tests/test_filters.py b/tests/test_filters.py
index 2c119c3..0843246 100644
--- a/tests/test_filters.py
+++ b/tests/test_filters.py
@@ -593,6 +593,21 @@ class TestFilter:
             "",
         ]
 
+    def test_groupby_default(self, env):
+        tmpl = env.from_string(
+            "{% for city, items in users|groupby('city', default='NY') %}"
+            "{{ city }}: {{ items|map(attribute='name')|join(', ') }}\n"
+            "{% endfor %}"
+        )
+        out = tmpl.render(
+            users=[
+                {"name": "emma", "city": "NY"},
+                {"name": "smith", "city": "WA"},
+                {"name": "john"},
+            ]
+        )
+        assert out == "NY: emma, john\nWA: smith\n"
+
     def test_filtertag(self, env):
         tmpl = env.from_string(
             "{% filter upper|replace('FOO', 'foo') %}foobar{% endfilter %}"