Unpack iterable class to its declared type for `iter` by flaeppe · Pull Request #14496 · python/mypy · GitHub

I've started an attempt to fix #14470. There's probably more stuff to be done here, as I've basically copy-pasted as much as I could of the behaviour of checker.TypeChecker.iterable_item_type.

mypy/mypy/checker.py

Lines 6347 to 6363 in cc1bcc9

    
           def iterable_item_type(self, instance: Instance) -> Type: 
        
               iterable = map_instance_to_supertype(instance, self.lookup_typeinfo("typing.Iterable")) 
        
               item_type = iterable.args[0] 
        
               if not isinstance(get_proper_type(item_type), AnyType): 
        
                   # This relies on 'map_instance_to_supertype' returning 'Iterable[Any]' 
        
                   # in case there is no explicit base class. 
        
                   return item_type 
        
               # Try also structural typing. 
        
               iter_type = get_proper_type(find_member("__iter__", instance, instance, is_operator=True)) 
        
               if iter_type and isinstance(iter_type, CallableType): 
        
                   ret_type = get_proper_type(iter_type.ret_type) 
        
                   if isinstance(ret_type, Instance): 
        
                       iterator = map_instance_to_supertype( 
        
                           ret_type, self.lookup_typeinfo("typing.Iterator") 
        
                       ) 
        
                       item_type = iterator.args[0] 
        
               return item_type

As that happened to resolve the issue I found. I'm not at all sure this is even a valid approach, I just wanted to check in on the idea before going any further. Any kind of feedback here would be much appreciated.

Fixes #14470

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

Unpack iterable class to its declared type

ad0e440

flaeppe mentioned this pull request Nov 28, 2023

Unpacking an iterable in a list comprehension leads to the type inferred as list[Any] #15747

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Unpack iterable class to its declared type for `iter` by flaeppe · Pull Request #14496 · python/mypy · GitHub

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Unpack iterable class to its declared type for iter - #14496

Unpack iterable class to its declared type for iter#14496
flaeppe wants to merge 1 commit into
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flaeppe:fix/varargs-from-class

flaeppe commented Jan 21, 2023

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	def iterable_item_type(self, instance: Instance) -> Type:
	iterable = map_instance_to_supertype(instance, self.lookup_typeinfo("typing.Iterable"))
	item_type = iterable.args[0]
	if not isinstance(get_proper_type(item_type), AnyType):
	# This relies on 'map_instance_to_supertype' returning 'Iterable[Any]'
	# in case there is no explicit base class.
	return item_type
	# Try also structural typing.
	iter_type = get_proper_type(find_member("__iter__", instance, instance, is_operator=True))
	if iter_type and isinstance(iter_type, CallableType):
	ret_type = get_proper_type(iter_type.ret_type)
	if isinstance(ret_type, Instance):
	iterator = map_instance_to_supertype(
	ret_type, self.lookup_typeinfo("typing.Iterator")
	)
	item_type = iterator.args[0]
	return item_type

Unpack iterable class to its declared type for `__iter__` by flaeppe · Pull Request #14496 · python/mypy · GitHub

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Unpack iterable class to its declared type for __iter__ - #14496

Unpack iterable class to its declared type for __iter__#14496flaeppe wants to merge 1 commit intopython:masterpython/mypy:masterfrom flaeppe:fix/varargs-from-classflaeppe/mypy:fix/varargs-from-classCopy head branch name to clipboard

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flaeppe commented Jan 21, 2023

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Unpack iterable class to its declared type for `iter` by flaeppe · Pull Request #14496 · python/mypy · GitHub

Unpack iterable class to its declared type for iter - #14496

Unpack iterable class to its declared type for iter#14496
flaeppe wants to merge 1 commit into
python:masterfrom
flaeppe:fix/varargs-from-class