Merge pull request #7387 from cool-RR/2020-06-11-raise-from

Fix exception causes all over the codebase

AUTHORS

@@ -233,6 +233,7 @@ Pulkit Goyal
 Punyashloka Biswal
 Quentin Pradet
 Ralf Schmitt
+Ram Rachum
 Ralph Giles
 Ran Benita
 Raphael Castaneda

changelog/7383.bugfix.rst

@@ -0,0 +1 @@
+Fixed exception causes all over the codebase, i.e. use `raise new_exception from old_exception` when wrapping an exception.

src/_pytest/_code/source.py

@@ -215,7 +215,7 @@ class Source:
             newex.offset = ex.offset
             newex.lineno = ex.lineno
             newex.text = ex.text
-            raise newex
+            raise newex from ex
         else:
             if flag & ast.PyCF_ONLY_AST:
                 assert isinstance(co, ast.AST)

src/_pytest/config/__init__.py

@@ -1189,8 +1189,8 @@ class Config:
     def _getini(self, name: str) -> Any:
         try:
             description, type, default = self._parser._inidict[name]
-        except KeyError:
-            raise ValueError("unknown configuration value: {!r}".format(name))
+        except KeyError as e:
+            raise ValueError("unknown configuration value: {!r}".format(name)) from e
         override_value = self._get_override_ini_value(name)
         if override_value is None:
             try:
@@ -1286,14 +1286,14 @@ class Config:
             if val is None and skip:
                 raise AttributeError(name)
             return val
-        except AttributeError:
+        except AttributeError as e:
             if default is not notset:
                 return default
             if skip:
                 import pytest
 
                 pytest.skip("no {!r} option found".format(name))
-            raise ValueError("no option named {!r}".format(name))
+            raise ValueError("no option named {!r}".format(name)) from e
 
     def getvalue(self, name, path=None):
         """ (deprecated, use getoption()) """

src/_pytest/config/argparsing.py

@@ -265,9 +265,9 @@ class Argument:
         else:
             try:
                 self.dest = self._short_opts[0][1:]
-            except IndexError:
+            except IndexError as e:
                 self.dest = "???"  # Needed for the error repr.
-                raise ArgumentError("need a long or short option", self)
+                raise ArgumentError("need a long or short option", self) from e
 
     def names(self) -> List[str]:
         return self._short_opts + self._long_opts

src/_pytest/config/findpaths.py

@@ -26,7 +26,7 @@ def _parse_ini_config(path: py.path.local) -> iniconfig.IniConfig:
     try:
         return iniconfig.IniConfig(path)
     except iniconfig.ParseError as exc:
-        raise UsageError(str(exc))
+        raise UsageError(str(exc)) from exc
 
 
 def load_config_dict_from_file(

src/_pytest/debugging.py

@@ -28,10 +28,10 @@ def _validate_usepdb_cls(value: str) -> Tuple[str, str]:
     """Validate syntax of --pdbcls option."""
     try:
         modname, classname = value.split(":")
-    except ValueError:
+    except ValueError as e:
         raise argparse.ArgumentTypeError(
             "{!r} is not in the format 'modname:classname'".format(value)
-        )
+        ) from e
     return (modname, classname)
 
 
@@ -130,7 +130,7 @@ class pytestPDB:
                 value = ":".join((modname, classname))
                 raise UsageError(
                     "--pdbcls: could not import {!r}: {}".format(value, exc)
-                )
+                ) from exc
         else:
             import pdb
 

src/_pytest/fixtures.py

@@ -938,13 +938,13 @@ def _eval_scope_callable(
         # Type ignored because there is no typing mechanism to specify
         # keyword arguments, currently.
         result = scope_callable(fixture_name=fixture_name, config=config)  # type: ignore[call-arg] # noqa: F821
-    except Exception:
+    except Exception as e:
         raise TypeError(
             "Error evaluating {} while defining fixture '{}'.\n"
             "Expected a function with the signature (*, fixture_name, config)".format(
                 scope_callable, fixture_name
             )
-        )
+        ) from e
     if not isinstance(result, str):
         fail(
             "Expected {} to return a 'str' while defining fixture '{}', but it returned:\n"

src/_pytest/logging.py

@@ -487,13 +487,13 @@ def get_log_level_for_setting(config: Config, *setting_names: str) -> Optional[i
         log_level = log_level.upper()
     try:
         return int(getattr(logging, log_level, log_level))
-    except ValueError:
+    except ValueError as e:
         # Python logging does not recognise this as a logging level
         raise pytest.UsageError(
             "'{}' is not recognized as a logging level name for "
             "'{}'. Please consider passing the "
             "logging level num instead.".format(log_level, setting_name)
-        )
+        ) from e
 
 
 # run after terminalreporter/capturemanager are configured

src/_pytest/monkeypatch.py

@@ -73,7 +73,7 @@ def resolve(name: str) -> object:
             if expected == used:
                 raise
             else:
-                raise ImportError("import error in {}: {}".format(used, ex))
+                raise ImportError("import error in {}: {}".format(used, ex)) from ex
         found = annotated_getattr(found, part, used)
     return found
 
@@ -81,12 +81,12 @@ def resolve(name: str) -> object:
 def annotated_getattr(obj: object, name: str, ann: str) -> object:
     try:
         obj = getattr(obj, name)
-    except AttributeError:
+    except AttributeError as e:
         raise AttributeError(
             "{!r} object at {} has no attribute {!r}".format(
                 type(obj).__name__, ann, name
             )
-        )
+        ) from e
     return obj
 
 

src/_pytest/python.py

@@ -551,8 +551,10 @@ class Module(nodes.File, PyCollector):
         importmode = self.config.getoption("--import-mode")
         try:
             mod = import_path(self.fspath, mode=importmode)
-        except SyntaxError:
-            raise self.CollectError(ExceptionInfo.from_current().getrepr(style="short"))
+        except SyntaxError as e:
+            raise self.CollectError(
+                ExceptionInfo.from_current().getrepr(style="short")
+            ) from e
         except ImportPathMismatchError as e:
             raise self.CollectError(
                 "import file mismatch:\n"
@@ -562,8 +564,8 @@ class Module(nodes.File, PyCollector):
                 "  %s\n"
                 "HINT: remove __pycache__ / .pyc files and/or use a "
                 "unique basename for your test file modules" % e.args
-            )
-        except ImportError:
+            ) from e
+        except ImportError as e:
             exc_info = ExceptionInfo.from_current()
             if self.config.getoption("verbose") < 2:
                 exc_info.traceback = exc_info.traceback.filter(filter_traceback)
@@ -578,7 +580,7 @@ class Module(nodes.File, PyCollector):
                 "Hint: make sure your test modules/packages have valid Python names.\n"
                 "Traceback:\n"
                 "{traceback}".format(fspath=self.fspath, traceback=formatted_tb)
-            )
+            ) from e
         except _pytest.runner.Skipped as e:
             if e.allow_module_level:
                 raise
@@ -587,7 +589,7 @@ class Module(nodes.File, PyCollector):
                 "To decorate a test function, use the @pytest.mark.skip "
                 "or @pytest.mark.skipif decorators instead, and to skip a "
                 "module use `pytestmark = pytest.mark.{skip,skipif}."
-            )
+            ) from e
         self.config.pluginmanager.consider_module(mod)
         return mod
 
@@ -836,8 +838,8 @@ class CallSpec2:
     def getparam(self, name: str) -> object:
         try:
             return self.params[name]
-        except KeyError:
-            raise ValueError(name)
+        except KeyError as e:
+            raise ValueError(name) from e
 
     @property
     def id(self) -> str:
@@ -1074,8 +1076,8 @@ class Metafunc:
         except TypeError:
             try:
                 iter(ids)
-            except TypeError:
-                raise TypeError("ids must be a callable or an iterable")
+            except TypeError as e:
+                raise TypeError("ids must be a callable or an iterable") from e
             num_ids = len(parameters)
 
         # num_ids == 0 is a special case: https://github.com/pytest-dev/pytest/issues/1849

src/_pytest/warnings.py

@@ -48,8 +48,8 @@ def _parse_filter(
             lineno = int(lineno_)
             if lineno < 0:
                 raise ValueError
-        except (ValueError, OverflowError):
-            raise warnings._OptionError("invalid lineno {!r}".format(lineno_))
+        except (ValueError, OverflowError) as e:
+            raise warnings._OptionError("invalid lineno {!r}".format(lineno_)) from e
     else:
         lineno = 0
     return (action, message, category, module, lineno)

testing/test_config.py

@@ -1778,5 +1778,5 @@ def test_conftest_import_error_repr(tmpdir):
     ):
         try:
             raise RuntimeError("some error")
-        except Exception:
-            raise ConftestImportFailure(path, sys.exc_info())
+        except Exception as e:
+            raise ConftestImportFailure(path, sys.exc_info()) from e

testing/test_runner.py

@@ -534,8 +534,8 @@ def test_outcomeexception_passes_except_Exception() -> None:
     with pytest.raises(outcomes.OutcomeException):
         try:
             raise outcomes.OutcomeException("test")
-        except Exception:
-            raise NotImplementedError()
+        except Exception as e:
+            raise NotImplementedError from e
 
 
 def test_pytest_exit() -> None: