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

@@ -11,16 +11,11 @@ from trytond.model import (
 from trytond.pyson import Eval, Bool
 from trytond.tools import decistmt
 from trytond.transaction import Transaction
-from trytond.modules.company.model import CompanyMultiValueMixin, CompanyValueMixin
+from trytond.modules.company.model import (
+    CompanyMultiValueMixin, CompanyValueMixin)
 
 from .exceptions import FormulaError
 
-__all__ = [
-    'AdvancePaymentTerm', 'AdvancePaymentTermLine',
-    'AdvancePaymentTermLineAccount',
-    'AdvancePaymentCondition', 'Sale', 'SaleLine',
-    'HandleInvoiceException']
-
 
 class AdvancePaymentTerm(
         DeactivableMixin, ModelSQL, ModelView):

setup.py

@@ -81,8 +81,8 @@ setup(name=name,
     keywords='tryton sale advance payment',
     package_dir={'trytond.modules.sale_advance_payment': '.'},
     packages=(
-        ['trytond.modules.sale_advance_payment'] +
-        ['trytond.modules.sale_advance_payment.%s' % p
+        ['trytond.modules.sale_advance_payment']
+        + ['trytond.modules.sale_advance_payment.%s' % p
             for p in find_packages()]
         ),
     package_data={
@@ -97,7 +97,8 @@ 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)',

stock.py

@@ -7,8 +7,6 @@ from trytond.pool import Pool, PoolMeta
 
 from .exceptions import ShippingBlocked
 
-__all__ = ['ShipmentOut']
-
 
 class ShipmentOut(metaclass=PoolMeta):
     __name__ = 'stock.shipment.out'

tests/__init__.py

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