Merge pull request #2251 from pallets/except-chain

use exception chaining

examples/cupoftee/pages.py

@@ -52,7 +52,7 @@ def process(self, id):
         try:
             self.server = self.cup.server_browser.servers[id]
         except KeyError:
-            raise NotFound()
+            raise NotFound() from None
 
 
 class Search(Page):

src/werkzeug/datastructures.py

@@ -578,19 +578,20 @@ def pop(self, key, default=_missing):
         except KeyError:
             if default is not _missing:
                 return default
-            raise exceptions.BadRequestKeyError(key)
+
+            raise exceptions.BadRequestKeyError(key) from None
 
     def popitem(self):
         """Pop an item from the dict."""
         try:
             item = dict.popitem(self)
 
             if len(item[1]) == 0:
-                raise exceptions.BadRequestKeyError(item)
+                raise exceptions.BadRequestKeyError(item[0])
 
             return (item[0], item[1][0])
         except KeyError as e:
-            raise exceptions.BadRequestKeyError(e.args[0])
+            raise exceptions.BadRequestKeyError(e.args[0]) from None
 
     def poplist(self, key):
         """Pop the list for a key from the dict.  If the key is not in the dict
@@ -607,7 +608,7 @@ def popitemlist(self):
         try:
             return dict.popitem(self)
         except KeyError as e:
-            raise exceptions.BadRequestKeyError(e.args[0])
+            raise exceptions.BadRequestKeyError(e.args[0]) from None
 
     def __copy__(self):
         return self.copy()
@@ -801,27 +802,34 @@ def pop(self, key, default=_missing):
         except KeyError:
             if default is not _missing:
                 return default
-            raise exceptions.BadRequestKeyError(key)
+
+            raise exceptions.BadRequestKeyError(key) from None
+
         for bucket in buckets:
             bucket.unlink(self)
+
         return buckets[0].value
 
     def popitem(self):
         try:
             key, buckets = dict.popitem(self)
         except KeyError as e:
-            raise exceptions.BadRequestKeyError(e.args[0])
+            raise exceptions.BadRequestKeyError(e.args[0]) from None
+
         for bucket in buckets:
             bucket.unlink(self)
+
         return key, buckets[0].value
 
     def popitemlist(self):
         try:
             key, buckets = dict.popitem(self)
         except KeyError as e:
-            raise exceptions.BadRequestKeyError(e.args[0])
+            raise exceptions.BadRequestKeyError(e.args[0]) from None
+
         for bucket in buckets:
             bucket.unlink(self)
+
         return key, [x.value for x in buckets]
 
 

src/werkzeug/local.py

@@ -54,7 +54,7 @@ class _CannotUseContextVar(Exception):
                 from gevent.monkey import is_object_patched
             except ImportError:
                 # Gevent isn't used, but Greenlet is and hasn't patched
-                raise _CannotUseContextVar()
+                raise _CannotUseContextVar() from None
             else:
                 if is_object_patched("threading", "local") and not is_object_patched(
                     "contextvars", "ContextVar"
@@ -162,7 +162,7 @@ def __getattr__(self, name: str) -> t.Any:
         try:
             return values[name]
         except KeyError:
-            raise AttributeError(name)
+            raise AttributeError(name) from None
 
     def __setattr__(self, name: str, value: t.Any) -> None:
         values = self._storage.get({}).copy()
@@ -175,7 +175,7 @@ def __delattr__(self, name: str) -> None:
             del values[name]
             self._storage.set(values)
         except KeyError:
-            raise AttributeError(name)
+            raise AttributeError(name) from None
 
 
 class LocalStack:
@@ -556,7 +556,8 @@ def _get_current_object(self) -> t.Any:
         try:
             return getattr(self.__local, self.__name)  # type: ignore
         except AttributeError:
-            raise RuntimeError(f"no object bound to {self.__name}")  # type: ignore
+            name = self.__name  # type: ignore
+            raise RuntimeError(f"no object bound to {name}") from None
 
     __doc__ = _ProxyLookup(  # type: ignore
         class_value=__doc__, fallback=lambda self: type(self).__doc__

src/werkzeug/routing.py

@@ -1591,10 +1591,12 @@ def bind(
             script_name = "/"
         if path_info is None:
             path_info = "/"
+
         try:
             server_name = _encode_idna(server_name)  # type: ignore
-        except UnicodeError:
-            raise BadHost()
+        except UnicodeError as e:
+            raise BadHost() from e
+
         return MapAdapter(
             self,
             server_name,
@@ -1973,13 +1975,13 @@ def match(
                         url_quote(e.path_info, self.map.charset, safe="/:|+"),
                         query_args,
                     )
-                )
+                ) from None
             except RequestAliasRedirect as e:
                 raise RequestRedirect(
                     self.make_alias_redirect_url(
                         path, rule.endpoint, e.matched_values, method, query_args
                     )
-                )
+                ) from None
             if rv is None:
                 continue
             if rule.methods is not None and method not in rule.methods:

src/werkzeug/serving.py

@@ -39,7 +39,7 @@
 
     class _SslDummy:
         def __getattr__(self, name: str) -> t.Any:
-            raise RuntimeError("SSL support unavailable")
+            raise RuntimeError("SSL support unavailable")  # noqa: B904
 
     ssl = _SslDummy()  # type: ignore
 
@@ -98,8 +98,8 @@ def read_chunk_len(self) -> int:
         try:
             line = self._rfile.readline().decode("latin1")
             _len = int(line.strip(), 16)
-        except ValueError:
-            raise OSError("Invalid chunk header")
+        except ValueError as e:
+            raise OSError("Invalid chunk header") from e
         if _len < 0:
             raise OSError("Negative chunk length not allowed")
         return _len
@@ -467,7 +467,9 @@ def generate_adhoc_ssl_pair(
         from cryptography.hazmat.primitives import hashes
         from cryptography.hazmat.primitives.asymmetric import rsa
     except ImportError:
-        raise TypeError("Using ad-hoc certificates requires the cryptography library.")
+        raise TypeError(
+            "Using ad-hoc certificates requires the cryptography library."
+        ) from None
 
     backend = default_backend()
     pkey = rsa.generate_private_key(

src/werkzeug/utils.py

@@ -847,7 +847,7 @@ def send_from_directory(
             raise NotFound()
     except ValueError:
         # path contains null byte on Python < 3.8
-        raise NotFound()
+        raise NotFound() from None
 
     return send_file(path, environ, **kwargs)
 
@@ -880,11 +880,13 @@ def import_string(import_name: str, silent: bool = False) -> t.Any:
         try:
             return getattr(module, obj_name)
         except AttributeError as e:
-            raise ImportError(e)
+            raise ImportError(e) from None
 
     except ImportError as e:
         if not silent:
-            raise ImportStringError(import_name, e).with_traceback(sys.exc_info()[2])
+            raise ImportStringError(import_name, e).with_traceback(
+                sys.exc_info()[2]
+            ) from None
 
     return None
 

tests/test_debug.py

@@ -230,7 +230,7 @@ def do_something():
             try:
                 do_something()
             except ValueError:
-                raise KeyError("outer")
+                raise KeyError("outer")  # noqa: B904
 
         debugged = DebuggedApplication(app)
         client = Client(debugged)
@@ -331,7 +331,7 @@ def test_chained_exception_cycle():
         try:
             raise ValueError()
         except ValueError:
-            raise TypeError()
+            raise TypeError()  # noqa: B904
     except TypeError as e:
         # create a cycle and make it available outside the except block
         e.__context__.__context__ = error = e