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elazarg opened this issue Oct 6, 2016 · 10 comments
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Type error in mypy? #2222

elazarg opened this issue Oct 6, 2016 · 10 comments
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@elazarg
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elazarg commented Oct 6, 2016

During #2221 (which I have little hope to be actually accepted) I ran into this function in binder.py:

    def get(self, expr: Union[Expression, Var]) -> Type:
        return self._get(expr.literal_hash)

The Var case comes from analyze_var_ref() in checkexpr.py.

Well, I couldn't find where Var.literal_hash is initialized to anything other than None, and returning None in the Var case passes all the tests. So I tried to replace it with something like the following:

    def get(self, expr: Union[Expression, Var]) -> Type:
        if isinstance(expr, Var):
            new_expr = NameExpr(expr.name())
        else:
            new_expr = expr
        return self._get(new_expr.literal_hash)

I then ran mypy on itself, but it raised many errors. So I ran the test suite, and I got many failures; however, it seems that these failures are due to a more precise typechecking. For example, take testModifyLoopFor4 (simplified):

x = None # type: Union[int, str]
x = 1

if 1:
    x = 'a'

The test does not say anything bad in this part, but mypy now complains that x is an int and therefore 'a' cannot be assigned into it. It might be too restrictive, but it is my understanding that this is the desired behavior, since "x=1" rebinds the variable into int (it's valid since int is part of the Union) and then it tries to rebind it to str, but now it is not possible.

I am not 100% sure, since I am not 100% sure how the code works and what is the expected behavior, but it looks like a bug - and if so, there are ~40 "type errors" to fix in the source code (although I suspect none of them is an actual error).

So what is the expected behavior? When and how should types rebind?
@elazarg
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elazarg commented Oct 6, 2016

Error messages about the source:

mypy/lex.py: note: In member "lex" of class "Lexer":
mypy/lex.py:361: error: Incompatible types in assignment (expression has type "str", variable has type "bytes")
mypy/lex.py:363: error: Argument 1 to "Bom" has incompatible type "int"; expected "str"
mypy/lex.py:364: error: Incompatible types in assignment (expression has type "Union[bytes, str]", variable has type "str")
mypy/lex.py:381: error: Argument 1 to "get" of "dict" has incompatible type "Union[int, str]"; expected "str"
mypy/test/data.py: note: In function "parse_test_data":
mypy/test/data.
8000
py:276: error: Incompatible types in assignment (expression has type "str", variable has type None)
mypy/types.py: note: In member "__init__" of class "TypeVarDef":
mypy/types.py:125: error: Incompatible types in assignment (expression has type "TypeVarId", variable has type "int")
mypy/types.py:126: error: Incompatible types in assignment (expression has type "Union[int, TypeVarId]", variable has type "TypeVarId")
mypy/types.py: note: In member "type_object" of class "CallableType":
mypy/types.py:635: error: Incompatible types in assignment (expression has type "Instance", variable has type "TupleType")
mypy/join.py: note: In function "join_simple":
mypy/join.py:41: error: Incompatible types in assignment (expression has type "Type", variable has type "NoneTyp")
mypy/join.py:44: error: Incompatible types in assignment (expression has type "Type", variable has type "UninhabitedType")
mypy/join.py: note: In function "join_types":
mypy/join.py:80: error: Incompatible types in assignment (expression has type "Type", variable has type "UnionType")
mypy/join.py:83: error: Incompatible types in assignment (expression has type "Type", variable has type "NoneTyp")
mypy/meet.py: note: In function "meet_types":
mypy/meet.py:24: error: Incompatible types in assignment (expression has type "Type", variable has type "UnionType")
mypy/meet.py: note: In function "is_overlapping_types":
mypy/meet.py:75: error: Incompatible types in assignment (expression has type "Type", variable has type "TypeVarType")
mypy/meet.py:77: error: Incompatible types in assignment (expression has type "Type", variable has type "TypeVarType")
mypy/binder.py: note: In member "get" of class "ConditionalTypeBinder":
mypy/binder.py:112: error: Incompatible types in assignment (expression has type "Expression", variable has type "NameExpr")  # that's an error in the fix...
mypy/checkmember.py: note: In function "analyze_member_access":
mypy/checkmember.py:109: error: Incompatible types in assignment (expression has type "Instance", variable has type "TupleType")
mypy/checkmember.py: note: In function "check_method_type":
mypy/checkmember.py:300: error: Incompatible types in assignment (expression has type "Instance", variable has type "TupleType")
mypy/checkmember.py: note: In function "map_type_from_supertype":
mypy/checkmember.py:487: error: Incompatible types in assignment (expression has type "Instance", variable has type "TupleType")
mypy/checkmember.py:492: error: Argument 1 to "map_instance_to_supertype" has incompatible type "Union[TupleType, Instance]"; expected "Instance"
mypy/checkexpr.py: note: In function "extract_refexpr_names":
mypy/checkexpr.py:73: error: Incompatible types in assignment (expression has type "RefExpr", variable has type "MemberExpr")
mypy/checkexpr.py: note: In member "analyze_ref_expr" of class "ExpressionChecker":
mypy/checkexpr.py:126: error: Incompatible types in assignment (expression has type "NoneTyp", variable has type "PartialType")
mypy/checkexpr.py:132: error: Incompatible types in assignment (expression has type "AnyType", variable has type "PartialType")
mypy/checkexpr.py: note: In member "infer_function_type_arguments_using_context" of class "ExpressionChecker":
mypy/checkexpr.py:461: error: Incompatible types in assignment (expression has type "NoneTyp", variable has type "TypeVarType")
mypy/checkexpr.py: note: In member "visit_tuple_expr" of class "ExpressionChecker":
mypy/checkexpr.py:1418: error: Incompatible types in assignment (expression has type "Type", variable has type "UnionType")
mypy/checkexpr.py: note: In member "infer_lambda_type_using_context" of class "ExpressionChecker":
mypy/checkexpr.py:1564: error: Incompatible types in assignment (expression has type "Type", variable has type "CallableType")
mypy/checkexpr.py: note: In function "overload_arg_similarity":
mypy/checkexpr.py:1961: error: Incompatible types in assignment (expression has type "Type", variable has type "TypeVarType")
mypy/checkexpr.py:1963: error: Incompatible types in assignment (expression has type "Type", variable has type "TypeVarType")
mypy/checkexpr.py:1996: error: Incompatible types in assignment (expression has type "Instance", variable has type "CallableType")
mypy/checkexpr.py:1998: error: Incompatible types in assignment (expression has type "Instance", variable has type "Overloaded")
mypy/checkexpr.py:2000: error: Incompatible types in assignment (expression has type "Instance", variable has type "TupleType")
mypy/checker.py: note: In member "check_assignment" of class "TypeChecker":
mypy/checker.py:1066: error: Incompatible types in assignment (expression has type "Type", variable has type "PartialType")
mypy/checker.py: note: In member "check_multi_assignment" of class "TypeChecker":
mypy/checker.py:1155: error: Incompatible types in assignment (expression has type "Expression", variable has type "StarExpr")
mypy/checker.py: note: In member "visit_decorator" of class "TypeChecker":
mypy/checker.py:1831: error: Incompatible types in assignment (expression has type "Type", variable has type "FunctionLike")
mypy/checker.py: note: In member "is_async_def" of class "TypeChecker":
mypy/checker.py:1982: error: Incompatible types in assignment (expression has type "Type", variable has type "Instance")
mypy/checker.py: note: In function "get_isinstance_type":
mypy/checker.py:2508: error: Incompatible types in assignment (expression has type "Type", variable has type "FunctionLike")

@rwbarton
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rwbarton commented Oct 6, 2016

The type of the variable x itself never changes. (What is known about) the type of the value of x can be different at different points in the program, since the value of x can change. But the variable always has type Union[int, str], so it's always legal to assign a str to it.

@elazarg
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elazarg commented Oct 6, 2016

So, what should happen in the code?

@rwbarton
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rwbarton commented Oct 6, 2016

The Var case of get shouldn't exist. The only caller is in analyze_var_ref but that is dead code. The type of a variable reference is actually refined from the binder elsewhere, in narrow_type_from_binder.

@elazarg
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elazarg commented Oct 6, 2016

Ok that makes sense

@gvanrossum
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Is there an action item here? Can you update the topic to reflect that? Else please close.

@elazarg
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elazarg commented Oct 13, 2016

There is, and it is fixed in #2238.

@gvanrossum gvanrossum mentioned this issue Oct 13, 2016
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@gvanrossum
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If you sent a separate PR that just fixed that it would be quicker to review.

@gvanrossum gvanrossum added this to the 0.5 milestone Oct 20, 2016
@rwbarton
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Plus it boosts your commit count :)

@elazarg
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elazarg commented Oct 25, 2016 •
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It just happens to be required for the PR I actually wanted.

@gvanrossum gvanrossum removed this from the 0.5 milestone Mar 29, 2017
@elazarg elazarg closed this as completed Apr 3, 2017
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