Fix flake8 errors and warnings

We add the flake8 configuration used so we ensure everyone uses the same.
We remove the usage of __all__ for non public API.
When possible, we rationalize the class name according to its __name__ and module.

issue9082
review297061002

.flake8

@@ -0,0 +1,2 @@
+[flake8]
+ignore=E123,E124,E126,E128,W503

sale.py

@@ -137,10 +137,12 @@ class SubscriptionLine(metaclass=PoolMeta):
                     | (other.start_date > line.start_date)
                     | (other.end_date > line.start_date)))
             | ((line.end_date != Null)
-                & (((other.end_date == Null)
+                & ((
+                        (other.end_date == Null)
                         & (other.start_date < line.end_date))
                     | ((other.end_date != Null)
-                        & (((other.end_date >= line.start_date)
+                        & ((
+                                (other.end_date >= line.start_date)
                                 & (other.end_date < line.end_date))
                             | ((other.start_date >= line.start_date)
                                 & (other.start_date < line.end_date)))))))

setup.py

@@ -79,8 +79,8 @@ setup(name=name,
     keywords='',
     package_dir={'trytond.modules.sale_subscription_asset': '.'},
     packages=(
-        ['trytond.modules.sale_subscription_asset'] +
-        ['trytond.modules.sale_subscription_asset.%s' % p
+        ['trytond.modules.sale_subscription_asset']
+        + ['trytond.modules.sale_subscription_asset.%s' % p
             for p in find_packages()]
         ),
     package_data={
@@ -95,7 +95,8 @@ setup(name=name,
         'Intended Audience :: Developers',
         'Intended Audience :: Financial and Insurance Industry',
         'Intended Audience :: Legal Industry',
-        'License :: OSI Approved :: GNU General Public License v3 or later (GPLv3+)',
+        'License :: OSI Approved :: '
+        'GNU General Public License v3 or later (GPLv3+)',
         'Natural Language :: Bulgarian',
         'Natural Language :: Catalan',
         'Natural Language :: Chinese (Simplified)',

tests/__init__.py

@@ -2,7 +2,7 @@
 # this repository contains the full copyright notices and license terms.
 
 try:
-    from trytond.modules.sale_subscription_asset.tests.test_sale_subscription_asset import suite
+    from trytond.modules.sale_subscription_asset.tests.test_sale_subscription_asset import suite  # noqa: E501
 except ImportError:
     from .test_sale_subscription_asset import suite