Merge pull request #53 from marier-nico/fix/get-dict-value

fix(util): fix get_value_at_path for None values

src/event_processor/exceptions.py

@@ -15,3 +15,7 @@ class InvocationError(EventProcessorError):
 
 class DependencyError(EventProcessorError):
     """Exceptions for failures while resolving dependencies."""
+
+
+class NoValueError(EventProcessorError):
+    """Exception for when a value is not present in a given context."""

src/event_processor/filters.py

@@ -3,7 +3,7 @@
 from typing import Any, Union, Callable
 
 from .dependencies import call_with_injection, Event
-from .exceptions import FilterError
+from .exceptions import FilterError, NoValueError
 from .util import get_value_at_path
 
 
@@ -78,7 +78,7 @@ def __init__(self, path: Any):
     def matches(self, event: dict) -> bool:
         try:
             get_value_at_path(event, self.path)
-        except KeyError:
+        except NoValueError:
             return False
 
         return True
@@ -102,7 +102,7 @@ def __init__(self, path: Any, value: Any):
     def matches(self, event: dict) -> bool:
         try:
             return self.value == get_value_at_path(event, self.path)
-        except KeyError:
+        except NoValueError:
             return False
 
     def __hash__(self):
@@ -132,7 +132,7 @@ def matches(self, event: dict) -> bool:
         try:
             found_value = get_value_at_path(event, self.path)
             float_value = float(found_value)
-        except (KeyError, ValueError):
+        except (NoValueError, ValueError):
             return False
 
         return self.comparator(float_value, self.target)

src/event_processor/util.py

@@ -4,18 +4,23 @@
 from types import ModuleType
 from typing import Any, List
 
+from .exceptions import NoValueError
+
 
 def get_value_at_path(source: dict, path: str) -> Any:
     """Get the value in a source dict at the given path.
 
     :param source: The dict from which to extract the value
     :param path: The path to look into
     :return: The value found at the path
-    :raises: KeyError when no value exists at the path
+    :raises: NoValueError when no value exists at the path
     """
     current_location = source
     for part in path.split("."):
-        current_location = current_location[part]
+        try:
+            current_location = current_location[part]
+        except (KeyError, TypeError):
+            raise NoValueError(f"No value at the path '{path}'")
 
     return current_location
 

src/tests/test_util.py

@@ -3,6 +3,7 @@
 
 import pytest
 
+from src.event_processor.exceptions import NoValueError
 from src.event_processor.util import get_value_at_path, py37_get_args, py37_get_origin, load_all_modules_in_package
 
 
@@ -18,10 +19,17 @@ def test_get_value_at_path_gets_the_value_when_it_exists():
 def test_get_value_at_path_raises_for_an_invalid_path():
     path = "a.b.c"
 
-    with pytest.raises(KeyError):
+    with pytest.raises(NoValueError):
         get_value_at_path({"a": {"b": {"not-c": None}}}, path)
 
 
+def test_get_value_at_path_raises_for_none_value():
+    path = "a.b.c"
+
+    with pytest.raises(NoValueError):
+        get_value_at_path({"a": None}, path)
+
+
 def test_py37_get_args_returns_generic_for_generic_type():
     assert py37_get_args(typing.Generic) is typing.Generic