Recursion error with nested Union #9657
Description
Crash Report
Many of my functions take Iter = Union[Iterator[T], Iterable[T]] as arguments. As for and many other functions in Python work with both iterators and iterables. However when I use Iter[Iter[T]] the code can break.
I've used Iter[Iter[Iter[int]]] as an example as Iter[Iter[T]] didn't break locally on the MVCE. Possibly due to a smaller existing stack.
from typing import Union, Iterator, Iterable
def bar(
values: Union[
Iterator[Union[
Iterator[Union[Iterator[int], Iterable[int]]],
Iterable[Union[Iterator[int], Iterable[int]]],
]],
Iterable[Union[
Iterator[Union[Iterator[int], Iterable[int]]],
Iterable[Union[Iterator[int], Iterable[int]]],
]],
]
) -> Iterator[int]:
for i in values:
for j in i:
for k in j:
yield k
bar([[[1]]])Traceback
$ mkdir example
$ cd example
$ vim test.py
$ mypy --show-traceback test.py >> traceback.txt
test.py:18: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.rtfd.io/en/latest/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.790
test.py:18: : note: use --pdb to drop into pdb
Traceback - it's long
$ cat traceback.txt
Traceback (most recent call last):
File "/usr/bin/mypy", line 33, in <module>
sys.exit(load_entry_point('mypy==0.790', 'console_scripts', 'mypy')())
File "/usr/lib/python3.8/site-packages/mypy/__main__.py", line 8, in console_entry
main(None, sys.stdout, sys.stderr)
File "/usr/lib/python3.8/site-packages/mypy/main.py", line 90, in main
res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
File "/usr/lib/python3.8/site-packages/mypy/build.py", line 180, in build
result = _build(
File "/usr/lib/python3.8/site-packages/mypy/build.py", line 254, in _build
graph = dispatch(sources, manager, stdout)
File "/usr/lib/python3.8/site-packages/mypy/build.py", line 2630, in dispatch
process_graph(graph, manager)
File "/usr/lib/python3.8/site-packages/mypy/build.py", line 2953, in process_graph
process_stale_scc(graph, scc, manager)
File "/usr/lib/python3.8/site-packages/mypy/build.py", line 3051, in process_stale_scc
graph[id].type_check_first_pass()
File "/usr/lib/python3.8/site-packages/mypy/build.py", line 2111, in type_check_first_pass
self.type_checker().check_first_pass()
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 294, in check_first_pass
self.accept(d)
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 401, in accept
stmt.accept(self)
File "/usr/lib/python3.8/site-packages/mypy/nodes.py", line 677, in accept
return visitor.visit_func_def(self)
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 726, in visit_func_def
self._visit_func_def(defn)
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 730, in _visit_func_def
self.check_func_item(defn, name=defn.name)
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 792, in check_func_item
self.check_func_def(defn, typ, name)
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 975, in check_func_def
self.accept(item.body)
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 401, in accept
stmt.accept(self)
File "/usr/lib/python3.8/site-packages/mypy/nodes.py", line 1005, in accept
return visitor.visit_block(self)
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 1973, in visit_block
self.accept(s)
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 401, in accept
stmt.accept(self)
File "/usr/lib/python3.8/site-packages/mypy/nodes.py", line 1130, in accept
return visitor.visit_for_stmt(self)
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 3479, in visit_for_stmt
iterator_type, item_type = self.analyze_iterable_item_type(s.expr)
File "/usr/lib/python3.8/site-packages/mypy/checker.py", line 3499, in analyze_iterable_item_type
iterator = echk.check_method_call_by_name('__iter__', iterable, [], [], expr)[0]
File "/usr/lib/python3.8/site-packages/mypy/checkexpr.py", line 2341, in check_method_call_by_name
return self.check_union_method_call_by_name(method, base_type,
File "/usr/lib/python3.8/site-packages/mypy/checkexpr.py", line 2373, in check_union_method_call_by_name
item, meth_item = self.check_method_call_by_name(method, typ, args, arg_kinds,
File "/usr/lib/python3.8/site-packages/mypy/checkexpr.py", line 2345, in check_method_call_by_name
method_type = analyze_member_access(method, base_type, context, False, False, True,
File "/usr/lib/python3.8/site-packages/mypy/checkmember.py", line 126, in analyze_member_access
result = _analyze_member_access(name, typ, mx, override_info)
File "/usr/lib/python3.8/site-packages/mypy/checkmember.py", line 143, in _analyze_member_access
return analyze_instance_member_access(name, typ, mx, override_info)
File "/usr/lib/python3.8/site-packages/mypy/checkmember.py", line 225, in analyze_instance_member_access
return analyze_member_var_access(name, typ, info, mx)
File "/usr/lib/python3.8/site-packages/mypy/checkmember.py", line 376, in analyze_member_var_access
return analyze_var(name, v, itype, info, mx, implicit=implicit)
File "/usr/lib/python3.8/site-packages/mypy/checkmember.py", line 578, in analyze_var
dispatched_type = meet.meet_types(mx.original_type, itype)
File "/usr/lib/python3.8/site-packages/mypy/meet.py", line 50, in meet_types
return t.accept(TypeMeetVisitor(s))
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 1724, in accept
return visitor.visit_union_type(self)
File "/usr/lib/python3.8/site-packages/mypy/meet.py", line 449, in visit_union_type
meets = [meet_types(x, self.s)
File "/usr/lib/python3.8/site-packages/mypy/meet.py", line 449, in <listcomp>
meets = [meet_types(x, self.s)
File "/usr/lib/python3.8/site-packages/mypy/meet.py", line 50, in meet_types
return t.accept(TypeMeetVisitor(s))
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/meet.py", line 505, in visit_instance
if is_subtype(t, self.s):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 93, in is_subtype
return _is_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 135, in _is_subtype
return left.accept(SubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 264, in visit_instance
if right.type.is_protocol and is_protocol_implementation(left, right):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 554, in is_protocol_implementation
is_compat = is_subtype(subtype, supertype, ignore_pos_arg_names=ignore_names)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 93, in is_subtype
return _is_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 135, in _is_subtype
return left.accept(SubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 1098, in accept
return visitor.visit_callable_type(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 299, in visit_callable_type
return is_callable_compatible(
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 857, in is_callable_compatible
if not ignore_return and not is_compat_return(left.ret_type, right.ret_type):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 193, in _is_subtype
return is_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 93, in is_subtype
return _is_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 135, in _is_subtype
return left.accept(SubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 258, in visit_instance
nominal = all(self.check_type_parameter(lefta, righta, tvar.variance)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 258, in <genexpr>
nominal = all(self.check_type_parameter(lefta, righta, tvar.variance)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 38, in check_type_parameter
return is_subtype(lefta, righta)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 93, in is_subtype
return _is_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 135, in _is_subtype
return left.accept(SubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 1724, in accept
return visitor.visit_union_type(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 464, in visit_union_type
return all(self._is_subtype(item, self.orig_right) for item in left.items)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 464, in <genexpr>
return all(self._is_subtype(item, self.orig_right) for item in left.items)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 193, in _is_subtype
return is_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 93, in is_subtype
return _is_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 118, in _is_subtype
is_subtype_of_item = any(is_subtype(orig_left, item,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 118, in <genexpr>
is_subtype_of_item = any(is_subtype(orig_left, item,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 93, in is_subtype
return _is_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 135, in _is_subtype
return left.accept(SubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 264, in visit_instance
if right.type.is_protocol and is_protocol_implementation(left, right):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 527, in is_protocol_implementation
if (mypy.sametypes.is_same_type(l, left)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 31, in is_same_type
return left.accept(SameTypeVisitor(right))
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 84, in visit_instance
is_same_types(left.args, self.right.args) and
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 45, in is_same_types
if not is_same_type(a1[i], a2[i]):
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 28, in is_same_type
left = simplify_union(left)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 37, in simplify_union
return make_simplified_union(t.items)
File "/usr/lib/python3.8/site-packages/mypy/typeops.py", line 366, in make_simplified_union
if i != j and is_proper_subtype(tj, ti, keep_erased_types=keep_erased):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1156, in is_proper_subtype
return _is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1177, in _is_proper_subtype
return left.accept(ProperSubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1273, in visit_instance
is_protocol_implementation(left, right, proper_subtype=True)):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 556, in is_protocol_implementation
is_compat = is_proper_subtype(subtype, supertype)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1156, in is_proper_subtype
return _is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1177, in _is_proper_subtype
return left.accept(ProperSubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 1098, in accept
return visitor.visit_callable_type(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1294, in visit_callable_type
return is_callable_compatible(left, right, is_compat=self._is_proper_subtype)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 857, in is_callable_compatible
if not ignore_return and not is_compat_return(left.ret_type, right.ret_type):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1207, in _is_proper_subtype
return is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1156, in is_proper_subtype
return _is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1177, in _is_proper_subtype
return left.accept(ProperSubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1267, in visit_instance
nominal = all(check_argument(ta, ra, tvar.variance) for ta, ra, tvar in
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1267, in <genexpr>
nominal = all(check_argument(ta, ra, tvar.variance) for ta, ra, tvar in
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1255, in check_argument
return self._is_proper_subtype(leftarg, rightarg)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1207, in _is_proper_subtype
return is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1156, in is_proper_subtype
return _is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1177, in _is_proper_subtype
return left.accept(ProperSubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 1724, in accept
return visitor.visit_union_type(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1356, in visit_union_type
return all([self._is_proper_subtype(item, self.orig_right) for item in left.items])
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1356, in <listcomp>
return all([self._is_proper_subtype(item, self.orig_right) for item in left.items])
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1207, in _is_proper_subtype
return is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1156, in is_proper_subtype
return _is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1172, in _is_proper_subtype
return any([is_proper_subtype(orig_left, item,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1172, in <listcomp>
return any([is_proper_subtype(orig_left, item,
# Start of recursion
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1156, in is_proper_subtype
return _is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1177, in _is_proper_subtype
return left.accept(ProperSubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1273, in visit_instance
is_protocol_implementation(left, right, proper_subtype=True)):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 527, in is_protocol_implementation
if (mypy.sametypes.is_same_type(l, left)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 31, in is_same_type
return left.accept(SameTypeVisitor(right))
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 84, in visit_instance
is_same_types(left.args, self.right.args) and
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 45, in is_same_types
if not is_same_type(a1[i], a2[i]):
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 28, in is_same_type
left = simplify_union(left)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 37, in simplify_union
return make_simplified_union(t.items)
File "/usr/lib/python3.8/site-packages/mypy/typeops.py", line 366, in make_simplified_union
if i != j and is_proper_subtype(tj, ti, keep_erased_types=keep_erased):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1156, in is_proper_subtype
return _is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1177, in _is_proper_subtype
return left.accept(ProperSubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1273, in visit_instance
is_protocol_implementation(left, right, proper_subtype=True)):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 527, in is_protocol_implementation
if (mypy.sametypes.is_same_type(l, left)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 31, in is_same_type
return left.accept(SameTypeVisitor(right))
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 84, in visit_instance
is_same_types(left.args, self.right.args) and
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 45, in is_same_types
if not is_same_type(a1[i], a2[i]):
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 28, in is_same_type
left = simplify_union(left)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 37, in simplify_union
return make_simplified_union(t.items)
File "/usr/lib/python3.8/site-packages/mypy/typeops.py", line 366, in make_simplified_union
if i != j and is_proper_subtype(tj, ti, keep_erased_types=keep_erased):
# Removed 30000 duplicate messages
File "/usr/lib/python3.8/site-packages/mypy/typeops.py", line 366, in make_simplified_union
if i != j and is_proper_subtype(tj, ti, keep_erased_types=keep_erased):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1156, in is_proper_subtype
return _is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1177, in _is_proper_subtype
return left.accept(ProperSubtypeVisitor(orig_right,
File "/usr/lib/python3.8/typing.py", line 873, in __new__
obj = super().__new__(cls)
RecursionError: maximum recursion depth exceeded while calling a Python object
To Reproduce
Playground. However, I'm not sure if these are the same errors. My local mypy results in a status 2 where the playground has status 139.
Existing issues
This error seems related to #6730 however the tracebacks are different. Whilst the crashes may be related I think this shows that the current code is exponential leading to crashes.
My recursive traceback
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1156, in is_proper_subtype
return _is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1177, in _is_proper_subtype
return left.accept(ProperSubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1273, in visit_instance
is_protocol_implementation(left, right, proper_subtype=True)):
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 527, in is_protocol_implementation
if (mypy.sametypes.is_same_type(l, left)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 31, in is_same_type
return left.accept(SameTypeVisitor(right))
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 84, in visit_instance
is_same_types(left.args, self.right.args) and
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 45, in is_same_types
if not is_same_type(a1[i], a2[i]):
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 28, in is_same_type
left = simplify_union(left)
File "/usr/lib/python3.8/site-packages/mypy/sametypes.py", line 37, in simplify_union
return make_simplified_union(t.items)
File "/usr/lib/python3.8/site-packages/mypy/typeops.py", line 366, in make_simplified_union
if i != j and is_proper_subtype(tj, ti, keep_erased_types=keep_erased):
6730 recursive traceback
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1156, in is_proper_subtype
return _is_proper_subtype(left, right,
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1177, in _is_proper_subtype
return left.accept(ProperSubtypeVisitor(orig_right,
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/subtypes.py", line 1261, in visit_instance
left = map_instance_to_supertype(left, right.type)
File "/usr/lib/python3.8/site-packages/mypy/maptype.py", line 24, in map_instance_to_supertype
return map_instance_to_supertypes(instance, superclass)[0]
File "/usr/lib/python3.8/site-packages/mypy/maptype.py", line 37, in map_instance_to_supertypes
a.extend(map_instance_to_direct_supertypes(t, sup))
File "/usr/lib/python3.8/site-packages/mypy/maptype.py", line 82, in map_instance_to_direct_supertypes
t = expand_type(b, env)
File "/usr/lib/python3.8/site-packages/mypy/expandtype.py", line 16, in expand_type
return typ.accept(ExpandTypeVisitor(env))
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 794, in accept
return visitor.visit_instance(self)
File "/usr/lib/python3.8/site-packages/mypy/expandtype.py", line 83, in visit_instance
args = self.expand_types(t.args)
File "/usr/lib/python3.8/site-packages/mypy/expandtype.py", line 143, in expand_types
a.append(t.accept(self))
File "/usr/lib/python3.8/site-packages/mypy/types.py", line 1724, in accept
return visitor.visit_union_type(self)
File "/usr/lib/python3.8/site-packages/mypy/expandtype.py", line 123, in visit_union_type
return make_simplified_union(self.expand_types(t.items), t.line, t.column)
File "/usr/lib/python3.8/site-packages/mypy/typeops.py", line 366, in make_simplified_union
if i != j and is_proper_subtype(tj, ti, keep_erased_types=keep_erased):
Caching
The error seems somewhat tempermental. If bar is proceeded with a subset of the type it seems some caching comes in to play. This runs without error.
from typing import Union, Iterator, Iterable
def foo(
values: Union[
Iterator[Union[Iterator[int], Iterable[int]]],
Iterable[Union[Iterator[int], Iterable[int]]],
]
) -> Iterator[int]:
for i in values:
for j in i:
yield j
def bar(
values: Union[
Iterator[Union[
Iterator[Union[Iterator[int], Iterable[int]]],
Iterable[Union[Iterator[int], Iterable[int]]],
]],
Iterable[Union[
Iterator[Union[Iterator[int], Iterable[int]]],
Iterable[Union[Iterator[int], Iterable[int]]],
]],
]
) -> Iterator[int]:
for i in values:
for j in i:
for k in j:
yield k
foo([[1]])
bar([[[1]]])