Use raise from e syntax for reraising exceptions

python/lsst/pex/config/config.py

@@ -729,13 +729,14 @@ def __get__(self, instance, owner=None, at=None, label="default"):
             # try statements are almost free in python if they succeed
             try:
                 return instance._storage[self.name]
-            except AttributeError:
+            except AttributeError as e:
                 if not isinstance(instance, Config):
                     return self
                 else:
-                    raise AttributeError(
+                    e.add_note(
                         f"Config {instance} is missing _storage attribute, likely incorrectly initialized"
                     )
+                    raise
 
     def __set__(
         self, instance: Config, value: FieldTypeVar | None, at: Any = None, label: str = "assignment"
@@ -790,7 +791,7 @@ def __set__(
             try:
                 self._validateValue(value)
             except BaseException as e:
-                raise FieldValidationError(self, instance, str(e))
+                raise FieldValidationError(self, instance, str(e)) from e
 
         instance._storage[self.name] = value
         if at is None:
@@ -1135,8 +1136,9 @@ def update(self, **kw):
             try:
                 field = self._fields[name]
                 field.__set__(self, value, at=at, label=label)
-            except KeyError:
-                raise KeyError(f"No field of name {name} exists in config type {_typeStr(self)}")
+            except KeyError as e:
+                e.add_note(f"No field of name {name} exists in config type {_typeStr(self)}")
+                raise
 
     def load(self, filename, root="config"):
         """Modify this config in place by executing the Python code in a

python/lsst/pex/config/configChoiceField.py

@@ -76,9 +76,9 @@ def __init__(self, dict_, value, at=None, label="assignment", setHistory=True):
                     if v not in self._dict:
                         # invoke __getitem__ to ensure it's present
                         self._dict.__getitem__(v, at=at)
-            except TypeError:
+            except TypeError as e:
                 msg = f"Value {value} is of incorrect type {_typeStr(value)}. Sequence type expected"
-                raise FieldValidationError(self._field, self._config, msg)
+                raise FieldValidationError(self._field, self._config, msg) from e
             self._set = set(value)
         else:
             self._set = set()
@@ -293,10 +293,10 @@ def __getitem__(self, k, at=None, label="default"):
         except KeyError:
             try:
                 dtype = self.types[k]
-            except Exception:
+            except Exception as e:
                 raise FieldValidationError(
                     self._field, self._config, f"Unknown key {k!r} in Registry/ConfigChoiceField"
-                )
+                ) from e
             name = _joinNamePath(self._config._name, self._field.name, k)
             if at is None:
                 at = getCallStack()
@@ -310,8 +310,8 @@ def __setitem__(self, k, value, at=None, label="assignment"):
 
         try:
             dtype = self.types[k]
-        except Exception:
-            raise FieldValidationError(self._field, self._config, f"Unknown key {k!r}")
+        except Exception as e:
+            raise FieldValidationError(self._field, self._config, f"Unknown key {k!r}") from e
 
         if value != dtype and type(value) is not dtype:
             msg = (

python/lsst/pex/config/configurableField.py

@@ -166,7 +166,7 @@ def retarget(self, target, ConfigClass=None, at=None, label="retarget"):
         try:
             ConfigClass = self._field.validateTarget(target, ConfigClass)
         except BaseException as e:
-            raise FieldValidationError(self._field, self._config, e.message)
+            raise FieldValidationError(self._field, self._config, e.message) from e
 
         if at is None:
             at = getCallStack()
@@ -304,8 +304,8 @@ def validateTarget(self, target, ConfigClass):
         if ConfigClass is None:
             try:
                 ConfigClass = target.ConfigClass
-            except Exception:
-                raise AttributeError("'target' must define attribute 'ConfigClass'")
+            except Exception as e:
+                raise AttributeError("'target' must define attribute 'ConfigClass'") from e
         if not issubclass(ConfigClass, Config):
             raise TypeError(
                 f"'ConfigClass' is of incorrect type {_typeStr(ConfigClass)}. "

python/lsst/pex/config/dictField.py

@@ -82,9 +82,9 @@ def __init__(self, config, field, value, at, label, setHistory=True):
                 for k in value:
                     # do not set history per-item
                     self.__setitem__(k, value[k], at=at, label=label, setHistory=False)
-            except TypeError:
+            except TypeError as e:
                 msg = f"Value {value} is of incorrect type {_typeStr(value)}. Mapping type expected."
-                raise FieldValidationError(self._field, self._config, msg)
+                raise FieldValidationError(self._field, self._config, msg) from e
         if setHistory:
             self._history.append((dict(self._dict), at, label))
 

python/lsst/pex/config/history.py

@@ -96,8 +96,8 @@ class Color:
     def __init__(self, text, category):
         try:
             color = Color.categories[category]
-        except KeyError:
-            raise RuntimeError(f"Unknown category: {category}")
+        except KeyError as e:
+            raise RuntimeError(f"Unknown category: {category}") from e
 
         self.rawText = str(text)
         x = color.lower().split(";")
@@ -109,8 +109,8 @@ def __init__(self, text, category):
 
         try:
             self._code = "%s" % (30 + Color.colors[self.color])
-        except KeyError:
-            raise RuntimeError(f"Unknown colour: {self.color}")
+        except KeyError as e:
+            raise RuntimeError(f"Unknown colour: {self.color}") from e
 
         if bold:
             self._code += ";1"

python/lsst/pex/config/listField.py

@@ -83,9 +83,9 @@ def __init__(self, config, field, value, at, label, setHistory=True):
             try:
                 for i, x in enumerate(value):
                     self.insert(i, x, setHistory=False)
-            except TypeError:
+            except TypeError as e:
                 msg = f"Value {value} is of incorrect type {_typeStr(value)}. Sequence type expected"
-                raise FieldValidationError(self._field, config, msg)
+                raise FieldValidationError(self._field, config, msg) from e
         if setHistory:
             self.history.append((list(self._list), at, label))
 

python/lsst/pex/config/wrap.py

@@ -201,8 +201,8 @@ def makeConfigClass(ctrl, name=None, base=Config, doc=None, module=None, cls=Non
                         nestedModuleObj = importlib.import_module(nestedModuleName)
                     try:
                         dtype = getattr(nestedModuleObj, ctype).ConfigClass
-                    except AttributeError:
-                        raise AttributeError(f"'{moduleName}.{ctype}.ConfigClass' does not exist")
+                    except AttributeError as e:
+                        raise AttributeError(f"'{moduleName}.{ctype}.ConfigClass' does not exist") from e
                     fields[k] = ConfigField(doc=doc, dtype=dtype)
                 else:
                     try: