Prevent use filter(lambda obj: test(obj), data)

In Python3 [1], if we need filter on python3, replace
filter(lambda obj: test(obj), data) with:
[obj for obj in data if test(obj)]. This patch replaces
filter function and introduces a hacking rule to prevent
using filter in future.

[1] https://wiki.openstack.org/wiki/Python3

Change-Id: I83d22108c02f8da007a7233e71a4a7fb833170ec

HACKING.rst

@@ -29,6 +29,8 @@ Neutron Specific Commandments
 - [N340] Check usage of <module>.i18n (and neutron.i18n)
 - [N341] Check usage of _ from python builtins
 - [N342] String interpolation should be delayed at logging calls.
+- [N344] Python 3: Do not use filter(lambda obj: test(obj), data). Replace it
+  with [obj for obj in data if test(obj)].
 
 Creating Unit Tests
 -------------------

neutron/hacking/checks.py

@@ -75,6 +75,7 @@ log_warn = re.compile(
     r"(.)*LOG\.(warn)\(\s*('|\"|_)")
 unittest_imports_dot = re.compile(r"\bimport[\s]+unittest\b")
 unittest_imports_from = re.compile(r"\bfrom[\s]+unittest\b")
+filter_match = re.compile(r".*filter\(lambda ")
 
 
 @flake8ext
@@ -381,6 +382,17 @@ def check_delayed_string_interpolation(logical_line, filename, noqa):
         yield(0, msg)
 
 
+@flake8ext
+def check_python3_no_filter(logical_line):
+    """N344 - Use list comprehension instead of filter(lambda)."""
+
+    msg = ("N343: Use list comprehension instead of "
+           "filter(lambda obj: test(obj), data) on python3.")
+
+    if filter_match.match(logical_line):
+        yield(0, msg)
+
+
 def factory(register):
     register(validate_log_translations)
     register(use_jsonutils)
@@ -400,3 +412,4 @@ def factory(register):
     register(check_builtins_gettext)
     register(check_unittest_imports)
     register(check_delayed_string_interpolation)
+    register(check_python3_no_filter)

neutron/objects/qos/policy.py

@@ -212,8 +212,8 @@ class QosPolicy(rbac_db.NeutronRbacObject):
 
     def obj_make_compatible(self, primitive, target_version):
         def filter_rules(obj_names, rules):
-            return filter(lambda rule:
-                          (rule['versioned_object.name'] in obj_names), rules)
+            return [rule for rule in rules if
+                    rule['versioned_object.name'] in obj_names]
 
         _target_version = versionutils.convert_version_to_tuple(target_version)
         names = []

neutron/policy.py

@@ -112,7 +112,7 @@ def _build_subattr_match_rule(attr_name, attr, action, target):
     # typing for API attributes
     # Expect a dict as type descriptor
     validate = attr['validate']
-    key = list(filter(lambda k: k.startswith('type:dict'), validate.keys()))
+    key = [k for k in validate.keys() if k.startswith('type:dict')]
     if not key:
         LOG.warning(_LW("Unable to find data type descriptor "
                         "for attribute %s"),

neutron/tests/tempest/api/test_subnetpools.py

@@ -110,13 +110,15 @@ class SubnetPoolsTest(SubnetPoolsTestBase):
         body = self._create_subnetpool(description='d1')
         self.assertEqual('d1', body['description'])
         sub_id = body['id']
-        body = filter(lambda x: x['id'] == sub_id,
-                      self.client.list_subnetpools()['subnetpools'])[0]
+        subnet_pools = [x for x in
+            self.client.list_subnetpools()['subnetpools'] if x['id'] == sub_id]
+        body = subnet_pools[0]
         self.assertEqual('d1', body['description'])
         body = self.client.update_subnetpool(sub_id, description='d2')
         self.assertEqual('d2', body['subnetpool']['description'])
-        body = filter(lambda x: x['id'] == sub_id,
-                      self.client.list_subnetpools()['subnetpools'])[0]
+        subnet_pools = [x for x in
+            self.client.list_subnetpools()['subnetpools'] if x['id'] == sub_id]
+        body = subnet_pools[0]
         self.assertEqual('d2', body['description'])
 
     @test.idempotent_id('741d08c2-1e3f-42be-99c7-0ea93c5b728c')

neutron/tests/unit/hacking/test_checks.py

@@ -339,6 +339,13 @@ class HackingTestCase(base.BaseTestCase):
         self.assertEqual(
             1, len(list(checks.check_log_warn_deprecated(bad, 'f'))))
 
+    def test_check_python3_filter(self):
+        f = checks.check_python3_no_filter
+        self.assertLineFails(f, "filter(lambda obj: test(obj), data)")
+        self.assertLinePasses(f, "[obj for obj in data if test(obj)]")
+        self.assertLinePasses(f, "filter(function, range(0,10))")
+        self.assertLinePasses(f, "lambda x, y: x+y")
+
 # The following is borrowed from hacking/tests/test_doctest.py.
 # Tests defined in docstring is easier to understand
 # in some cases, for example, hacking rules which take tokens as argument.