Add check for redundant import aliases

This adds a pep8 function that will check for redundant import aliases.
Any imports of the forms below will not be allowed.

from x import y as y
import x as x
import x.y as y

Change-Id: Iff90f0172d97bd1d49d54c811a70c8af11776da4

HACKING.rst

@@ -66,6 +66,7 @@ Nova Specific Commandments
 - [N357] Use oslo_utils.uuidutils or uuidsentinel(in case of test cases) to
   generate UUID instead of uuid4().
 - [N358] Return must always be followed by a space when returning a value.
+- [N359] Check for redundant import aliases.
 
 Creating Unit Tests
 -------------------

nova/hacking/checks.py

@@ -98,6 +98,7 @@ log_remove_context = re.compile(
     r"(.)*LOG\.(.*)\(.*(context=[_a-zA-Z0-9].*)+.*\)")
 return_not_followed_by_space = re.compile(r"^\s*return(?:\(|{|\"|'|#).*$")
 uuid4_re = re.compile(r"uuid4\(\)($|[^\.]|\.hex)")
+redundant_import_alias_re = re.compile(r"import (?:.*\.)?(.+) as \1$")
 
 
 class BaseASTChecker(ast.NodeVisitor):
@@ -801,6 +802,21 @@ def return_followed_by_space(logical_line):
                "N357: Return keyword should be followed by a space.")
 
 
+def no_redundant_import_alias(logical_line):
+    """Check for redundant import aliases.
+
+    Imports should not be in the forms below.
+
+    from x import y as y
+    import x as x
+    import x.y as y
+
+    N359
+    """
+    if re.search(redundant_import_alias_re, logical_line):
+        yield (0, "N359: Import alias should not be redundant.")
+
+
 def factory(register):
     register(import_no_db_in_virt)
     register(no_db_session_in_public_api)
@@ -842,3 +858,4 @@ def factory(register):
     register(no_assert_true_false_is_not)
     register(check_uuid4)
     register(return_followed_by_space)
+    register(no_redundant_import_alias)

nova/service.py

@@ -96,7 +96,7 @@ def setup_profiler(binary, host):
 
 
 def assert_eventlet_uses_monotonic_clock():
-    import eventlet.hubs as hubs
+    from eventlet import hubs
     import monotonic
 
     hub = hubs.get_hub()

nova/tests/unit/image/test_glance.py

@@ -22,7 +22,7 @@ from cursive import exception as cursive_exception
 import ddt
 import glanceclient.exc
 from glanceclient.v1 import images
-import glanceclient.v2.schemas as schemas
+from glanceclient.v2 import schemas
 from keystoneauth1 import loading as ks_loading
 import mock
 import six

nova/tests/unit/test_hacking.py

@@ -782,3 +782,23 @@ class HackingTestCase(test.NoDBTestCase):
             "return ' some string '"))))
         self.assertEqual(0, len(list(checks.return_followed_by_space(
             "return (int('40') + 2)"))))
+
+    def test_no_redundant_import_alias(self):
+        code = """
+                  from x import y as y
+                  import x as x
+                  import x.y.z as z
+                  import x.y.z as y.z
+               """
+        errors = [(x + 1, 0, 'N359') for x in range(4)]
+        self._assert_has_errors(code, checks.no_redundant_import_alias,
+                                expected_errors=errors)
+        code = """
+                  from x import y
+                  import x
+                  from x.y import z
+                  from a import bcd as cd
+                  import ab.cd.efg as fg
+                  import ab.cd.efg as d.efg
+               """
+        self._assert_has_no_errors(code, checks.no_redundant_import_alias)

nova/tests/unit/virt/test_virt_drivers.py

@@ -82,14 +82,11 @@ class _FakeDriverBackendTestCase(object):
         else:
             self.saved_libvirt = None
 
-        import nova.tests.unit.virt.libvirt.fake_imagebackend as \
+        from nova.tests.unit.virt.libvirt import fake_imagebackend
-            fake_imagebackend
+        from nova.tests.unit.virt.libvirt import fake_libvirt_utils
-        import nova.tests.unit.virt.libvirt.fake_libvirt_utils as \
+        from nova.tests.unit.virt.libvirt import fakelibvirt
-            fake_libvirt_utils
-        import nova.tests.unit.virt.libvirt.fakelibvirt as fakelibvirt
 
-        import nova.tests.unit.virt.libvirt.fake_os_brick_connector as \
+        from nova.tests.unit.virt.libvirt import fake_os_brick_connector
-            fake_os_brick_connector
 
         self.useFixture(fake_imagebackend.ImageBackendFixture())
         self.useFixture(fakelibvirt.FakeLibvirtFixture())