ensure single import per line

This adds the very small plugin flake8-import-single which
will prevent us from having an import with more than one symbol
on a line.

Flake8 by itself prevents this pattern with E401:

import collections, os, sys

However does not do anything with this:

from sqlalchemy import Column, text

Both statements have the same issues generating merge artifacts
as well as presenting a manual decision to be made.   While
zimports generally cleans up such imports at the top level, we
don't enforce zimports / pre-commit use.

the plugin finds the same issue for imports that are inside of
test methods.   We shouldn't usually have imports in test methods
so most of them here are moved to be top level.

The version is pinned at 0.1.5; the project seems to have no
activity since 2019, however there are three 0.1.6dev releases
on pypi which stopped in September 2019, they seem to be
experiments with packaging.  The source for 0.1.5
is extremely simple and only reveals one method to flake8
(the run() method).

Change-Id: Icea894e43bad9c0b5d4feb5f49c6c666d6ea6aa1

2 files changed, 14 insertions, 9 deletions

diff --git a/examples/custom_attributes/active_column_defaults.py b/examples/custom_attributes/active_column_defaults.py
index dea79ee95..d5322d331 100644
--- a/examples/custom_attributes/active_column_defaults.py
+++ b/examples/custom_attributes/active_column_defaults.py
@@ -5,7 +5,15 @@ when an un-set attribute is accessed.
 
 """
 
+import datetime
+
+from sqlalchemy import Column
+from sqlalchemy import create_engine
+from sqlalchemy import DateTime
 from sqlalchemy import event
+from sqlalchemy import Integer
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.orm import Session
 
 
 def configure_listener(mapper, class_):
@@ -67,11 +75,6 @@ def default_listener(col_attr, default):
 
 if __name__ == "__main__":
 
-    from sqlalchemy import Column, Integer, DateTime, create_engine
-    from sqlalchemy.orm import Session
-    from sqlalchemy.ext.declarative import declarative_base
-    import datetime
-
     Base = declarative_base()
 
     event.listen(Base, "mapper_configured", configure_listener, propagate=True)
diff --git a/examples/custom_attributes/listen_for_events.py b/examples/custom_attributes/listen_for_events.py
index b2d2b690b..a94a3dab2 100644
--- a/examples/custom_attributes/listen_for_events.py
+++ b/examples/custom_attributes/listen_for_events.py
@@ -3,7 +3,13 @@ and listen for change events.
 
 """
 
+from sqlalchemy import Column
 from sqlalchemy import event
+from sqlalchemy import ForeignKey
+from sqlalchemy import Integer
+from sqlalchemy import String
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.orm import relationship
 
 
 def configure_listener(class_, key, inst):
@@ -23,10 +29,6 @@ def configure_listener(class_, key, inst):
 
 if __name__ == "__main__":
 
-    from sqlalchemy import Column, Integer, String, ForeignKey
-    from sqlalchemy.orm import relationship
-    from sqlalchemy.ext.declarative import declarative_base
-
     class Base:
         def receive_change_event(self, verb, key, value, oldvalue):
             s = "Value '%s' %s on attribute '%s', " % (value, verb, key)