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

@@ -2,11 +2,11 @@
 # this repository contains the full copyright notices and license terms.
 
 from trytond.pool import Pool
-from .purchase import *
+from . import purchase
 
 
 def register():
     Pool.register(
-        ProductSupplier,
-        ProductSupplierDay,
+        purchase.ProductSupplier,
+        purchase.ProductSupplierDay,
         module='stock_supply_day', type_='model')

purchase.py

@@ -5,8 +5,6 @@ from trytond.model import ModelSQL, fields
 from trytond.pool import PoolMeta, Pool
 from trytond.transaction import Transaction
 
-__all__ = ['ProductSupplier', 'ProductSupplierDay']
-
 
 class ProductSupplier(metaclass=PoolMeta):
     __name__ = 'purchase.product_supplier'

setup.py

@@ -78,8 +78,8 @@ setup(name=name,
     keywords='tryton supply day',
     package_dir={'trytond.modules.stock_supply_day': '.'},
     packages=(
-        ['trytond.modules.stock_supply_day'] +
-        ['trytond.modules.stock_supply_day.%s' % p for p in find_packages()]
+        ['trytond.modules.stock_supply_day']
+        + ['trytond.modules.stock_supply_day.%s' % p for p in find_packages()]
         ),
     package_data={
         'trytond.modules.stock_supply_day': (info.get('xml', [])
@@ -92,7 +92,8 @@ setup(name=name,
         'Intended Audience :: Developers',
         '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.stock_supply_day.tests.test_stock_supply_day import suite
+    from trytond.modules.stock_supply_day.tests.test_stock_supply_day import suite  # noqa: E501
 except ImportError:
     from .test_stock_supply_day import suite