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

__init__.py

@@ -2,10 +2,10 @@
 # this repository contains the full copyright notices and license terms.
 
 from trytond.pool import Pool
-from .sale import *
+from . import sale
 
 
 def register():
     Pool.register(
-        Sale,
+        sale.Sale,
         module='sale_stock_quantity', type_='model')

sale.py

@@ -12,9 +12,6 @@ from trytond.tools import grouped_slice
 from .exceptions import StockQuantityError, StockQuantityWarning
 
 
-__all__ = ['Sale']
-
-
 class Sale(metaclass=PoolMeta):
     __name__ = 'sale.sale'
 

setup.py

@@ -82,8 +82,9 @@ setup(name=name,
     keywords='tryton sale stock',
     package_dir={'trytond.modules.sale_stock_quantity': '.'},
     packages=(
-        ['trytond.modules.sale_stock_quantity'] +
-        ['trytond.modules.sale_stock_quantity.%s' % p for p in find_packages()]
+        ['trytond.modules.sale_stock_quantity']
+        + ['trytond.modules.sale_stock_quantity.%s' % p
+            for p in find_packages()]
         ),
     package_data={
         'trytond.modules.sale_stock_quantity': (info.get('xml', [])
@@ -98,7 +99,8 @@ setup(name=name,
         'Intended Audience :: Financial and Insurance Industry',
         'Intended Audience :: Legal Industry',
         'Intended Audience :: Manufacturing',
-        '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_stock_quantity.tests.test_sale_stock_quantity import suite
+    from trytond.modules.sale_stock_quantity.tests.test_sale_stock_quantity import suite  # noqa: E501
 except ImportError:
     from .test_sale_stock_quantity import suite