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

purchase.py

@@ -17,13 +17,6 @@ from trytond.wizard import Wizard, StateView, StateTransition, Button
 from .exceptions import PreviousQuotation
 
 
-__all__ = ['Configuration', 'ConfigurationSequence', 'Quotation',
-    'QuotationLine', 'CreatePurchaseRequestQuotationAskSuppliers',
-    'CreatePurchaseRequestQuotationSucceed', 'PurchaseRequest',
-    'CreatePurchaseRequestQuotation', 'CreatePurchase',
-    'PurchaseRequestQuotationReport']
-
-
 def process_request(func):
     @wraps(func)
     def wrapper(cls, quotations):
@@ -625,7 +618,8 @@ class CreatePurchase(Wizard):
         to_save = []
         requests = Request.browse(Transaction().context['active_ids'])
 
-        reqs = [r for r in requests if not r.purchase_line and r.quotation_lines]
+        reqs = [r for r in requests
+            if not r.purchase_line and r.quotation_lines]
         to_save = []
         for req in reqs:
             if req.best_quotation_line:

setup.py

@@ -83,8 +83,8 @@ setup(name=name,
     keywords='tryton purchase request for quotation',
     package_dir={'trytond.modules.purchase_request_quotation': '.'},
     packages=(
-        ['trytond.modules.purchase_request_quotation'] +
-        ['trytond.modules.purchase_request_quotation.%s' % p
+        ['trytond.modules.purchase_request_quotation']
+        + ['trytond.modules.purchase_request_quotation.%s' % p
             for p in find_packages()]
         ),
     package_data={

tests/__init__.py

@@ -3,7 +3,7 @@
 # the full copyright notices and license terms.
 
 try:
-    from trytond.modules.purchase_request_quotation.tests.test_purchase_request_quotation import suite
+    from trytond.modules.purchase_request_quotation.tests.test_purchase_request_quotation import suite  # noqa: E501
 except ImportError:
     from .test_purchase_request_quotation import suite