Allow using del keyword to mark unused variables (#279)

Co-authored-by: Sergei Shishov <[email protected]>
Co-authored-by: Jendrik Seipp <[email protected]>

CHANGELOG.md

@@ -3,6 +3,7 @@
 * Print absolute filepaths as relative again (as with 2.1 and before) if they
   are below the current directory (The-Compiler, #246).
 * Run tests and add PyPI trove for Python 3.10 (chayim, #266).
+* Allow using the `del` keyword to mark unused variables (sshishov, #279).
 
 # 2.3 (2021-01-16)
 

README.md

@@ -108,9 +108,20 @@ check that all whitelisted code actually still exists in your project.
 **Marking unused variables**
 
 There are situations where you can't just remove unused variables, e.g.,
-in tuple assignments or function signatures. Vulture will ignore these
-variables if they start with an underscore (e.g., `_x, y = get_pos()` or
-`def my_method(self, widget, **_kwargs)`).
+in function signatures. The recommended solution is to use the `del`
+keyword as described in the
+[PyLint manual](http://pylint-messages.wikidot.com/messages:w0613) and on
+[StackOverflow](https://stackoverflow.com/a/14836005):
+
+```python
+def foo(x, y):
+    del y
+    return x + 3
+```
+
+Vulture will also ignore all variables that start with an underscore, so
+you can use `_x, y = get_pos()` to mark unused tuple assignments or
+function arguments, e.g., `def foo(x, _y)`.
 
 **Minimum confidence**
 

tests/test_scavenging.py

@@ -741,3 +741,21 @@ def bad():
         assert not v.found_dead_code_or_error
     else:
         assert v.found_dead_code_or_error
+
+
+def test_unused_args_with_del(v):
+    v.scan(
+        """\
+def foo(a, b, c, d=3):
+    del c, d
+    return a + b
+
+foo(1, 2)
+"""
+    )
+
+    check(v.defined_funcs, ["foo"])
+    check(v.defined_vars, ["a", "b", "c", "d"])
+    check(v.used_names, ["foo", "a", "b", "c", "d"])
+    check(v.unused_vars, [])
+    check(v.unused_funcs, [])

vulture/core.py

@@ -609,7 +609,7 @@ def visit_ImportFrom(self, node):
 
     def visit_Name(self, node):
         if (
-            isinstance(node.ctx, ast.Load)
+            isinstance(node.ctx, (ast.Load, ast.Del))
             and node.id not in IGNORED_VARIABLE_NAMES
         ):
             self.used_names.add(node.id)