support __slots__ #1268
Description
__slots__ is already handled specially in ty, but should be more fully supported in line with the Python specification.
__slots__ may not be a very commonly used feature, but several major libraries use it (e.g. attrs), and supporting it could improve inference results and error reporting.
Here are the features that should be implemented:
- Assume that the attributes defined in
__slots__are not unresolved - Attempting to read/write/declare an attribute that is not defined in
__slots__will be reported as an error - Defining a class variable to set a default value for a name that is defined in
__slots__will be reported as an error - Remove
__dict__and__weakref__from classes that define__slots__ - An error will be raised if nonempty
__slots__are defined for a class derived from a "variable-length" built-in type such as int, bytes, and tuple
class C:
__slots__ = ("foo",)
def __init__(self, foo, bar):
self.foo = foo
self.bar = bar # error
baz: int # error (pyright doesn't report this as an error)
foo: int = 1 # error
class D:
__slots__ = ("bar",)
d = D()
reveal_type(d.bar) # revealed: Any or Unknown
reveal_type(d.foo) # error
d.bar = 1 # ok
# Classes with `__slots__` defined will not have a `__dict__` by default.
d.foo = 1 # error
class E:
__slots__ = ("foo", "__dict__")
def __init__(self, foo, bar):
self.foo = foo
self.bar = bar # ok
# `F` has `__dict__` and `__weakref__`.
class F: ...
# Even if a class defines `__slots__`, if the superclass has `__dict__` or `__weakref__`,
# those attributes will be inherited.
class G(F):
__slots__ = ("foo",)
def __init__(self, foo, bar):
self.foo = foo
self.bar = bar # ok
# error: nonempty __slots__ not supported for subtype of 'int'
class H(int):
__slots__ = ("foo",)related: #111