8000 gh-122311: Improve and unify pickle errors by serhiy-storchaka · Pull Request #122771 · python/cpython · GitHub
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gh-122311: Improve and unify pickle errors #122771

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Merged
merged 2 commits into from
Sep 9, 2024
Merged

gh-122311: Improve and unify pickle errors #122771

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43d94f2
gh-122311: Improve and unify pickle errors
serhiy-storchaka Aug 5, 2024
3f43170
Merge branch 'main' into pickle-errors
serhiy-storchaka Sep 3, 2024
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90 changes: 49 additions & 41 deletions Lib/pickle.py
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Original file line number Diff line number Diff line change
Expand Up @@ -322,7 +322,9 @@ def whichmodule(obj, name):
"""Find the module an object belong to."""
dotted_path = name.split('.')
module_name = getattr(obj, '__module__', None)
if module_name is None and '<locals>' not in dotted_path:
if '<locals>' in dotted_path:
raise PicklingError(f"Can't pickle local object {obj!r}")
if module_name is None:
# Protect the iteration by using a list copy of sys.modules against dynamic
# modules that trigger imports of other modules upon calls to getattr.
for module_name, module in sys.modules.copy().items():
Expand All @@ -336,22 +338,21 @@ def whichmodule(obj, name):
except AttributeError:
pass
module_name = '__main__'
elif module_name is None:
module_name = '__main__'

try:
__import__(module_name, level=0)
module = sys.modules[module_name]
except (ImportError, ValueError, KeyError) as exc:
raise PicklingError(f"Can't pickle {obj!r}: {exc!s}")
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Should we do from None or from exc here (and in the other cases below?)

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No, removing from None was intentional. Error here is not normal. The original exception and its traceback can add additional context.

We use from None if the details of the original exception are not important. For example when it is a result of using EAFP instead of LBYL. But in this case we expect that the object can be found by name, and if this fails, we want to know gore details.

try:
if _getattribute(module, dotted_path) is obj:
return module_name
except (ImportError, KeyError, AttributeError):
raise PicklingError(
"Can't pickle %r: it's not found as %s.%s" %
(obj, module_name, name)) from None
except AttributeError:
raise PicklingError(f"Can't pickle {obj!r}: "
f"it's not found as {module_name}.{name}")

raise PicklingError(
"Can't pickle %r: it's not the same object as %s.%s" %
(obj, module_name, name))
f"Can't pickle {obj!r}: it's not the same object as {module_name}.{name}")

def encode_long(x):
r"""Encode a long to a two's complement little-endian binary string.
Expand Down Expand Up @@ -403,6 +404,13 @@ def decode_long(data):
"""
return int.from_bytes(data, byteorder='little', signed=True)

def _T(obj):
cls = type(obj)
module = cls.__module__
if module in (None, 'builtins', '__main__'):
return cls.__qualname__
return f'{module}.{cls.__qualname__}'


_NoValue = object()

Expand Down Expand Up @@ -585,8 +593,7 @@ def save(self, obj, save_persistent_id=True):
if reduce is not _NoValue:
rv = reduce()
else:
raise PicklingError("Can't pickle %r object: %r" %
(t.__name__, obj))
raise PicklingError(f"Can't pickle {_T(t)} object")

# Check for string returned by reduce(), meaning "save as global"
if isinstance(rv, str):
Expand All @@ -595,13 +602,13 @@ def save(self, obj, save_persistent_id=True):

# Assert that reduce() returned a tuple
if not isinstance(rv, tuple):
raise PicklingError("%s must return string or tuple" % reduce)
raise PicklingError(f'__reduce__ must return a string or tuple, not {_T(rv)}')

# Assert that it returned an appropriately sized tuple
l = len(rv)
if not (2 <= l <= 6):
raise PicklingError("Tuple returned by %s must have "
"two to six elements" % reduce)
raise PicklingError("tuple returned by __reduce__ "
"must contain 2 through 6 elements")

# Save the reduce() output and finally memoize the object
self.save_reduce(obj=obj, *rv)
Expand All @@ -626,10 +633,12 @@ def save_reduce(self, func, args, state=None, listitems=None,
dictitems=None, state_setter=None, *, obj=None):
# This API is called by some subclasses

if not isinstance(args, tuple):
raise PicklingError("args from save_reduce() must be a tuple")
if not callable(func):
raise PicklingError("func from save_reduce() must be callable")
raise PicklingError(f"first item of the tuple returned by __reduce__ "
f"must be callable, not {_T(func)}")
if not isinstance(args, tuple):
raise PicklingError(f"second item of the tuple returned by __reduce__ "
f"must be a tuple, not {_T(args)}")

save = self.save
write = self.write
Expand All @@ -638,11 +647,10 @@ def save_reduce(self, func, args, state=None, listitems=None,
if self.proto >= 2 and func_name == "__newobj_ex__":
cls, args, kwargs = args
if not hasattr(cls, "__new__"):
raise PicklingError("args[0] from {} args has no __new__"
.format(func_name))
raise PicklingError("first argument to __newobj_ex__() has no __new__")
if obj is not None and cls is not obj.__class__:
raise PicklingError("args[0] from {} args has the wrong class"
.format(func_name))
raise PicklingError(f"first argument to __newobj_ex__() "
f"must be {obj.__class__!r}, not {cls!r}")
if self.proto >= 4:
save(cls)
save(args)
Expand Down Expand Up @@ -682,11 +690,10 @@ def save_reduce(self, func, args, state=None, listitems=None,
# Python 2.2).
cls = args[0]
if not hasattr(cls, "__new__"):
raise PicklingError(
"args[0] from __newobj__ args has no __new__")
raise PicklingError("first argument to __newobj__() has no __new__")
if obj is not None and cls is not obj.__class__:
raise PicklingError(
"args[0] from __newobj__ args has the wrong class")
raise PicklingError(f"first argument to __newobj__() "
f"must be {obj.__class__!r}, not {cls!r}")
args = args[1:]
save(cls)
save(args)
Expand Down Expand Up @@ -1133,8 +1140,7 @@ def save_global(self, obj, name=None):
def _save_toplevel_by_name(self, module_name, name):
if self.proto >= 3:
# Non-ASCII identifiers are supported only with protocols >= 3.
self.write(GLOBAL + bytes(module_name, "utf-8") + b'\n' +
bytes(name, "utf-8") + b'\n')
encoding = "utf-8"
else:
if self.fix_imports:
r_name_mapping = _compat_pickle.REVERSE_NAME_MAPPING
Expand All @@ -1143,13 +1149,19 @@ def _save_toplevel_by_name(self, module_name, name):
module_name, name = r_name_mapping[(module_name, name)]
elif module_name in r_import_mapping:
module_name = r_import_mapping[module_name]
try:
self.write(GLOBAL + bytes(module_name, "ascii") + b'\n' +
bytes(name, "ascii") + b'\n')
except UnicodeEncodeError:
raise PicklingError(
"can't pickle global identifier '%s.%s' using "
"pickle protocol %i" % (module_name, name, self.proto)) from None
encoding = "ascii"
try:
self.write(GLOBAL + bytes(module_name, encoding) + b'\n')
except UnicodeEncodeError:
raise PicklingError(
f"can't pickle module identifier {module_name!r} using "
f"pickle protocol {self.proto}")
try:
self.write(bytes(name, encoding) + b'\n')
except UnicodeEncodeError:
raise PicklingError(
f"can't pickle global identifier {name!r} using "
f"pickle protocol {self.proto}")

def save_type(self, obj):
if obj is type(None):
Expand Down Expand Up @@ -1609,17 +1621,13 @@ def find_class(self, module, name):
elif module in _compat_pickle.IMPORT_MAPPING:
module = _compat_pickle.IMPORT_MAPPING[module]
__import__(module, level=0)
if self.proto >= 4:
module = sys.modules[module]
if self.proto >= 4 and '.' in name:
dotted_path = name.split('.')
if '<locals>' in dotted_path:
raise AttributeError(
f"Can't get local attribute {name!r} on {module!r}")
try:
return _getattribute(module, dotted_path)
return _getattribute(sys.modules[module], dotted_path)
except AttributeError:
raise AttributeError(
f"Can't get attribute {name!r} on {module!r}") from None
f"Can't resolve path {name!r} on module {module!r}")
else:
return getattr(sys.modules[module], name)

Expand Down
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