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

account.py

@@ -103,10 +103,10 @@ class Tax(metaclass=PoolMeta):
         periods = context.get('periods', [])
         where = super(Tax, cls)._amount_where(tax_line, move_line, move)
         return ((where
-                & (tax_line.on_cash_basis == False)
+                & (tax_line.on_cash_basis == Literal(False))
                 | (tax_line.on_cash_basis == Null))
             | ((tax_line.period.in_(periods) if periods else Literal(False))
-                & (tax_line.on_cash_basis == True)))
+                & (tax_line.on_cash_basis == Literal(True))))
 
     @classmethod
     def _amount_domain(cls):

setup.py

@@ -79,8 +79,8 @@ setup(name=name,
     keywords='tryton account tax cash',
     package_dir={'trytond.modules.account_tax_cash': '.'},
     packages=(
-        ['trytond.modules.account_tax_cash'] +
-        ['trytond.modules.account_tax_cash.%s' % p for p in find_packages()]
+        ['trytond.modules.account_tax_cash']
+        + ['trytond.modules.account_tax_cash.%s' % p for p in find_packages()]
         ),
     package_data={
         'trytond.modules.account_tax_cash': (info.get('xml', [])
@@ -94,7 +94,8 @@ 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 :: Czech',

tests/__init__.py

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