Expand C416 to dict comprehensions (#490)

Co-authored-by: Adam Johnson <me@adamj.eu>

CHANGELOG.rst

@@ -2,6 +2,10 @@
 Changelog
 =========
 
+* Expand C416 to ``dict`` comprehensions.
+
+  Thanks to Aaron Gokaslan in `PR #490 <https://github.com/adamchainz/flake8-comprehensions/pull/490>`__.
+
 3.10.1 (2022-10-29)
 -------------------
 

README.rst

@@ -150,13 +150,14 @@ For example:
 * Rewrite ``sorted(iterable)[::-1]`` as ``sorted(iterable, reverse=True)``
 * Rewrite ``reversed(iterable[::-1])`` as ``iterable``
 
-C416: Unnecessary ``<list/set>`` comprehension - rewrite using ``<list/set>``\().
----------------------------------------------------------------------------------
+C416: Unnecessary ``<dict/list/set>`` comprehension - rewrite using ``<dict/list/set>``\().
+-------------------------------------------------------------------------------------------
 
-It's unnecessary to use a list comprehension if the elements are unchanged.
-The iterable should be wrapped in ``list()`` or ``set()`` instead.
+It's unnecessary to use a dict/list/set comprehension to build a data structure if the elements are unchanged.
+Wrap the iterable with ``dict()``, ``list()``, or ``set()`` instead.
 For example:
 
+* Rewrite ``{a: b for a, b in iterable}`` as ``dict(iterable)``
 * Rewrite ``[x for x in iterable]`` as ``list(iterable)``
 * Rewrite ``{x for x in iterable}`` as ``set(iterable)``
 

src/flake8_comprehensions/__init__.py

@@ -295,15 +295,29 @@ def run(self) -> Generator[tuple[int, int, str, type[Any]], None, None]:
                             type(self),
                         )
 
-            elif isinstance(node, (ast.ListComp, ast.SetComp)):
+            elif isinstance(node, (ast.DictComp, ast.ListComp, ast.SetComp)):
                 if (
                     len(node.generators) == 1
                     and not node.generators[0].ifs
                     and not node.generators[0].is_async
                     and (
-                        isinstance(node.elt, ast.Name)
-                        and isinstance(node.generators[0].target, ast.Name)
-                        and node.elt.id == node.generators[0].target.id
+                        (
+                            isinstance(node, (ast.ListComp, ast.SetComp))
+                            and isinstance(node.elt, ast.Name)
+                            and isinstance(node.generators[0].target, ast.Name)
+                            and node.elt.id == node.generators[0].target.id
+                        )
+                        or (
+                            isinstance(node, ast.DictComp)
+                            and isinstance(node.key, ast.Name)
+                            and isinstance(node.value, ast.Name)
+                            and isinstance(node.generators[0].target, ast.Tuple)
+                            and len(node.generators[0].target.elts) == 2
+                            and isinstance(node.generators[0].target.elts[0], ast.Name)
+                            and node.generators[0].target.elts[0].id == node.key.id
+                            and isinstance(node.generators[0].target.elts[1], ast.Name)
+                            and node.generators[0].target.elts[1].id == node.value.id
+                        )
                     )
                 ):
                     yield (

tests/test_flake8_comprehensions.py

@@ -757,6 +757,10 @@ def test_C415_fail(code, failures, flake8_path):
 @pytest.mark.parametrize(
     "code",
     [
+        "{x, y for x, y, z in zip('abc', '123', 'def')}",
+        "{y: x for x, y in zip('abc', '123')}",
+        "{x: y for x, (y,) in zip('a', ('1',))}",
+        "{x: z for x, (y,), z in zip('a', ('1',), 'b')}",
         "[str(x) for x in range(5)]",
         "[x + 1 for x in range(5)]",
         "[x for x in range(5) if x % 2]",
@@ -796,6 +800,20 @@ def test_C416_pass(code, flake8_path):
 @pytest.mark.parametrize(
     "code,failures",
     [
+        (
+            "{x: y for x, y in zip(range(5), range(5))}",
+            [
+                "./example.py:1:1: C416 Unnecessary dict comprehension - "
+                + "rewrite using dict().",
+            ],
+        ),
+        (
+            "{x: y for (x, y) in zip(range(5), range(5))}",
+            [
+                "./example.py:1:1: C416 Unnecessary dict comprehension - "
+                + "rewrite using dict().",
+            ],
+        ),
         (
             "[x for x in range(5)]",
             [