Fix type hinting for ErrorPolicy's children

Type hint Type[ErrorPolicy] was not resoling correctly for its children.

Author: mamiksik

CHANGELOG.md

@@ -29,6 +29,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Race condition in `test_types_repository_separation` - Martin Miksik
 - Import error while using python version prior to 3.7 - Martin Miksik
 - Parsing datetime containing timezone information for python 3.6 and lower - Martin Miksik
+- Type hinting for ErrorPolicy's children - Martin Miksik
 
 ## [1.3.0]
 

pyodata/config.py

@@ -1,7 +1,7 @@
 """ Contains definition of configuration class for PyOData"""
 
 from typing import Type, Dict
-from pyodata.policies import PolicyFatal, ParserError, ErrorPolicy
+from pyodata.policies import PolicyFatal, ParserError, ErrorPolicyType
 import pyodata.version
 
 
@@ -14,8 +14,8 @@ class Config:
 
     def __init__(self,
                  odata_version: Type[pyodata.version.ODATAVersion],
-                 custom_error_policies=None,
-                 default_error_policy=None,
+                 custom_error_policies: Dict[ParserError, ErrorPolicyType] = None,
+                 default_error_policy: ErrorPolicyType = None,
                  xml_namespaces=None
                  ):
 
@@ -48,19 +48,19 @@ def __init__(self,
         self._annotation_namespaces = None
         self._aliases: Dict[str, str] = dict()
 
-    def err_policy(self, error: ParserError) -> ErrorPolicy:
+    def err_policy(self, error: ParserError) -> ErrorPolicyType:
         """ Returns error policy for given error. If custom error policy fo error is set, then returns that."""
         if self._custom_error_policy is None:
             return self._default_error_policy
 
         return self._custom_error_policy.get(error, self._default_error_policy)
 
-    def set_default_error_policy(self, policy: ErrorPolicy):
+    def set_default_error_policy(self, policy: ErrorPolicyType):
         """ Sets default error policy as well as resets custom error policies"""
         self._custom_error_policy = None
         self._default_error_policy = policy
 
-    def set_custom_error_policy(self, policies: Dict[ParserError, Type[ErrorPolicy]]):
+    def set_custom_error_policy(self, policies: Dict[ParserError, ErrorPolicyType]):
         """ Sets custom error policy. It should be called only after setting default error policy, otherwise
             it has no effect. See implementation of "set_default_error_policy" for more details.
         """

pyodata/policies.py

@@ -6,6 +6,7 @@
 import logging
 from abc import ABC, abstractmethod
 from enum import Enum, auto
+from typing import TypeVar
 
 
 class ParserError(Enum):
@@ -22,6 +23,9 @@ class ParserError(Enum):
     COMPLEX_TYPE = auto()
 
 
+ErrorPolicyType = TypeVar("ErrorPolicyType", bound="ErrorPolicy")
+
+
 class ErrorPolicy(ABC):
     """ All policies has to inhere this class"""
     @abstractmethod