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 .currency import *
+from . import currency
 
 
 def register():
     Pool.register(
-        Currency,
-        Rate,
+        currency.Currency,
+        currency.CurrencyRate,
         module='currency', type_='model')

currency.py

@@ -17,8 +17,6 @@ from trytond.pyson import Eval
 
 from .exceptions import RateError
 
-__all__ = ['Currency', 'Rate']
-
 
 class Currency(DeactivableMixin, ModelSQL, ModelView):
     'Currency'
@@ -223,8 +221,8 @@ class Currency(DeactivableMixin, ModelSQL, ModelView):
         return query
 
 
-class Rate(ModelSQL, ModelView):
-    'Rate'
+class CurrencyRate(ModelSQL, ModelView):
+    "Currency Rate"
     __name__ = 'currency.currency.rate'
     date = fields.Date('Date', required=True, select=True,
         help="From when the rate applies.")
@@ -236,7 +234,7 @@ class Rate(ModelSQL, ModelView):
 
     @classmethod
     def __setup__(cls):
-        super(Rate, cls).__setup__()
+        super().__setup__()
         t = cls.__table__()
         cls._sql_constraints = [
             ('date_currency_uniq', Unique(t, t.date, t.currency),

setup.py

@@ -79,8 +79,8 @@ setup(name=name,
     keywords='tryton currency',
     package_dir={'trytond.modules.currency': '.'},
     packages=(
-        ['trytond.modules.currency'] +
-        ['trytond.modules.currency.%s' % p for p in find_packages()]
+        ['trytond.modules.currency']
+        + ['trytond.modules.currency.%s' % p for p in find_packages()]
         ),
     package_data={
         'trytond.modules.currency': (info.get('xml', [])
@@ -95,7 +95,8 @@ 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)',
@@ -139,7 +140,7 @@ setup(name=name,
     currency = trytond.modules.currency
     [console_scripts]
     trytond_import_currencies = trytond.modules.currency.scripts.import_currencies:run [data]
-    """,
+    """,  # noqa: E501
     test_suite='tests',
     test_loader='trytond.test_loader:Loader',
     tests_require=tests_require,