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bpo-40336: Refactor typing._SpecialForm #19620
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Original file line number | Diff line number | Diff line change |
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@@ -141,8 +141,9 @@ def _type_check(arg, msg, is_argument=True): | |
if (isinstance(arg, _GenericAlias) and | ||
arg.__origin__ in invalid_generic_forms): | ||
raise TypeError(f"{arg} is not valid as type argument") | ||
if (isinstance(arg, _SpecialForm) and arg not in (Any, NoReturn) or | ||
arg in (Generic, Protocol)): | ||
if arg in (Any, NoReturn): | ||
return arg | ||
if isinstance(arg, _SpecialForm) or arg in (Generic, Protocol): | ||
raise TypeError(f"Plain {arg} is not valid as type argument") | ||
if isinstance(arg, (type, TypeVar, ForwardRef)): | ||
return arg | ||
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@@ -299,51 +300,22 @@ def __deepcopy__(self, memo): | |
return self | ||
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< 10000 span class='blob-code-inner blob-code-marker js-skip-tagsearch' data-code-marker="-">class _SpecialForm(_Final, _Immutable, _root=True): | ||
"""Internal indicator of special typing constructs. | ||
See _doc instance attribute for specific docs. | ||
""" | ||
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__slots__ = ('_name', '_doc') | ||
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def __new__(cls, *args, **kwds): | ||
"""Constructor. | ||
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This only exists to give a better error message in case | ||
someone tries to subclass a special typing object (not a good idea). | ||
""" | ||
if (len(args) == 3 and | ||
isinstance(args[0], str) and | ||
isinstance(args[1], tuple)): | ||
# Close enough. | ||
raise TypeError(f"Cannot subclass {cls!r}") | ||
return super().__new__(cls) | ||
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def __init__(self, name, doc): | ||
self._name = name | ||
self._doc = doc | ||
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@property | ||
def __doc__(self): | ||
return self._doc | ||
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def __eq__(self, other): | ||
if not isinstance(other, _SpecialForm): | ||
return NotImplemented | ||
return self._name == other._name | ||
# Internal indicator of special typing constructs. | ||
# See __doc__ instance attribute for specific docs. | ||
class _SpecialForm(_Final, _root=True): | ||
__slots__ = ('_name', '__doc__', '_getitem') | ||
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def __hash__(self): | ||
return hash((self._name,)) | ||
def __init__(self, getitem): | ||
self._getitem = getitem | ||
self._name = getitem.__name__ | ||
self.__doc__ = getitem.__doc__ | ||
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def __repr__(self): | ||
return 'typing.' + self._name | ||
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def __reduce__(self): | ||
return self._name | ||
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def __call__(self, *args, **kwds): | ||
raise TypeError(f"Cannot instantiate {self!r}") | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Again, a custom exception message may be helpful, but not important. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Your are right. " There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Perfect! Thanks for fixing this. |
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def __instancecheck__(self, obj): | ||
raise TypeError(f"{self} cannot be used with isinstance()") | ||
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@@ -352,31 +324,10 @@ def __subclasscheck__(self, cls): | |
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@_tp_cache | ||
def __getitem__(self, parameters): | ||
if self._name in ('ClassVar', 'Final'): | ||
item = _type_check(parameters, f'{self._name} accepts only single type.') | ||
return _GenericAlias(self, (item,)) | ||
if self._name == 'Union': | ||
if parameters == (): | ||
raise TypeError("Cannot take a Union of no types.") | ||
if not isinstance(parameters, tuple): | ||
parameters = (parameters,) | ||
msg = "Union[arg, ...]: each arg must be a type." | ||
parameters = tuple(_type_check(p, msg) for p in parameters) | ||
parameters = _remove_dups_flatten(parameters) | ||
if len(parameters) == 1: | ||
return parameters[0] | ||
return _GenericAlias(self, parameters) | ||
if self._name == 'Optional': | ||
arg = _type_check(parameters, "Optional[t] requires a single type.") | ||
return Union[arg, type(None)] | ||
if self._name == 'Literal': | ||
# There is no '_type_check' call because arguments to Literal[...] are | ||
# values, not types. | ||
return _GenericAlias(self, parameters) | ||
raise TypeError(f"{self} is not subscriptable") | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Splitting this is really great. I always wanted to do this, but didn't find a way to do this that wouldn't require boilerplate code, it looks like you have found such way. |
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Any = _SpecialForm('Any', doc= | ||
return self._getitem(self, parameters) | ||
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@_SpecialForm | ||
def Any(self, parameters): | ||
"""Special type indicating an unconstrained type. | ||
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- Any is compatible with every type. | ||
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@@ -386,9 +337,11 @@ def __getitem__(self, parameters): | |
Note that all the above statements are true from the point of view of | ||
static type checkers. At runtime, Any should not be used with instance | ||
or class checks. | ||
""") | ||
""" | ||
raise TypeError(f"{self} is not subscriptable") | ||
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NoReturn = _SpecialForm('NoReturn', doc= | ||
@_SpecialForm | ||
def NoReturn(self, parameters): | ||
"""Special type indicating functions that never return. | ||
Example:: | ||
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@@ -399,9 +352,11 @@ def stop() -> NoReturn: | |
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This type is invalid in other positions, e.g., ``List[NoReturn]`` | ||
will fail in static type checkers. | ||
""") | ||
""" | ||
raise TypeError(f"{self} is not subscriptable") | ||
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ClassVar = _SpecialForm('ClassVar', doc= | ||
@_SpecialForm | ||
def ClassVar(self, parameters): | ||
"""Special type construct to mark class variables. | ||
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An annotation wrapped in ClassVar indicates that a given | ||
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@@ -416,9 +371,12 @@ class Starship: | |
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Note that ClassVar is not a class itself, and should not | ||
be used with isinstance() or issubclass(). | ||
""") | ||
""" | ||
item = _type_check(parameters, f'{self} accepts only single type.') | ||
return _GenericAlias(self, (item,)) | ||
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Final = _SpecialForm('Final', doc= | ||
@_SpecialForm | ||
def Final(self, parameters): | ||
"""Special typing construct to indicate final names to type checkers. | ||
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A final name cannot be re-assigned or overridden in a subclass. | ||
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@@ -434,9 +392,12 @@ class FastConnector(Connection): | |
TIMEOUT = 1 # Error reported by type checker | ||
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There is no runtime checking of these properties. | ||
""") | ||
""" | ||
item = _type_check(parameters, f'{self} accepts only single type.') | ||
return _GenericAlias(self, (item,)) | ||
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Union = _SpecialForm('Union', doc= | ||
@_SpecialForm | ||
def Union(self, parameters): | ||
"""Union type; Union[X, Y] means either X or Y. | ||
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To define a union, use e.g. Union[int, str]. Details: | ||
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@@ -461,15 +422,29 @@ class FastConnector(Connection): | |
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- You cannot subclass or instantiate a union. | ||
- You can use Optional[X] as a shorthand for Union[X, None]. | ||
""") | ||
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Optional = _SpecialForm('Optional', doc= | ||
""" | ||
if parameters == (): | ||
raise TypeError("Cannot take a Union of no types.") | ||
if not isinstance(parameters, tuple): | ||
parameters = (parameters,) | ||
msg = "Union[arg, ...]: each arg must be a type." | ||
parameters = tuple(_type_check(p, msg) for p in parameters) | ||
parameters = _remove_dups_flatten(parameters) | ||
if len(parameters) == 1: | ||
return parameters[0] | ||
return _GenericAlias(self, parameters) | ||
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@_SpecialForm | ||
def Optional(self, parameters): | ||
"""Optional type. | ||
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Optional[X] is equivalent to Union[X, None]. | ||
""") | ||
""" | ||
arg = _type_check(parameters, f"{self} requires a single type.") | ||
return Union[arg, type(None)] | ||
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Literal = _SpecialForm('Literal', doc= | ||
@_SpecialForm | ||
def Literal(self, parameters): | ||
"""Special typing form to define literal types (a.k.a. value types). | ||
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This form can be used to indicate to type checkers that the corresponding | ||
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@@ -486,10 +461,13 @@ def open_helper(file: str, mode: MODE) -> str: | |
open_helper('/some/path', 'r') # Passes type check | ||
open_helper('/other/path', 'typo') # Error in type checker | ||
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Literal[...] cannot be subclassed. At runtime, an arbitrary value | ||
is allowed as type argument to Literal[...], but type checkers may | ||
impose restrictions. | ||
""") | ||
Literal[...] cannot be subclassed. At runtime, an arbitrary value | ||
is allowed as type argument to Literal[...], but type checkers may | ||
impose restrictions. | ||
""" | ||
# There is no '_type_check' call because arguments to Literal[...] are | ||
# values, not types. | ||
return _GenericAlias(self, parameters) | ||
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class ForwardRef(_Final, _root=True): | ||
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It would be good to keep a custom error message, but not important.
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You are right, I tested again
class A(Any): pass
, and got "__init__() takes 2 positional arguments but 4 were given
" which does not look user friendly.But the former message was "
Cannot subclass <class 'typing._SpecialForm'>
" which does not look correct, because we subclass an instance of_SpecialForm
, not_SpecialForm
itself. It is not possible to fix in__new__
, but we can raise better error in custom__mro_entries__
.There was a problem hiding this comment.
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Using
__mro_entries__
is a great idea!