[FIX] account,base: python 3.8 compatibility

Remove warnings
Add mandatory parameter posonlyargs

closes odoo/odoo#40396

X-original-commit: aeb1e592a6fbc918fb4edf4a8953aa375124337d
Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>

addons/account/models/account.py

@@ -1350,7 +1350,7 @@ class AccountTax(models.Model):
 
     @api.onchange('amount_type')
     def onchange_amount_type(self):
-        if self.amount_type is not 'group':
+        if self.amount_type != 'group':
             self.children_tax_ids = [(5,)]
         if self.amount_type == 'group':
             self.description = None

odoo/addons/base/models/qweb.py

@@ -94,6 +94,7 @@ class Contextifier(ast.NodeTransformer):
                 # handle that cross-version
                 kwonlyargs=[],
                 kw_defaults=[],
+                posonlyargs=[],
             ),
             body=Contextifier(self._safe_names + tuple(names)).visit(node.body)
         ), node)
@@ -542,7 +543,7 @@ class QWeb(object):
                 ast.arg(arg='values', annotation=None),
                 ast.arg(arg='options', annotation=None),
                 ast.arg(arg='log', annotation=None),
-            ], defaults=[], vararg=None, kwarg=None, kwonlyargs=[], kw_defaults=[]),
+            ], defaults=[], vararg=None, kwarg=None, posonlyargs=[], kwonlyargs=[], kw_defaults=[]),
             body=body or [ast.Return()],
             decorator_list=[])
         if lineno is not None:

odoo/addons/base/models/res_config.py

@@ -597,7 +597,7 @@ class ResConfigSettings(models.TransientModel, ResConfigModuleInstallationMixin)
         # other fields: execute method 'set_values'
         # Methods that start with `set_` are now deprecated
         for method in dir(self):
-            if method.startswith('set_') and method is not 'set_values':
+            if method.startswith('set_') and method != 'set_values':
                 _logger.warning(_('Methods that start with `set_` are deprecated. Override `set_values` instead (Method %s)') % method)
 
     def execute(self):