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Fix typechecking on Python 3.8 #7953

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merged 1 commit into from
Nov 14, 2019
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Fix typechecking on Python 3.8 #7953

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9 changes: 6 additions & 3 deletions mypy/fastparse.py
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Original file line number Diff line number Diff line change
Expand Up @@ -321,13 +321,16 @@ def set_line(self, node: N, n: Union[ast3.expr, ast3.stmt]) -> N:
node.end_line = getattr(n, "end_lineno", None) if isinstance(n, ast3.expr) else None
return node

def translate_expr_list(self, l: Sequence[AST]) -> List[Expression]:
res = [] # type: List[Expression]
def translate_opt_expr_list(self, l: Sequence[Optional[AST]]) -> List[Optional[Expression]]:
res = [] # type: List[Optional[Expression]]
for e in l:
exp = self.visit(e)
res.append(exp)
return res

def translate_expr_list(self, l: Sequence[AST]) -> List[Expression]:
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Maybe you can use an overload instead?

@overload
def translate_expr_list(l: Sequence[AST]) -> List[Expression]: ...
@overload
def translate_expr_list(l: Sequence[Optional[AST]]) -> List[Optional[Expression]]: ...

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I tried that first and it complained that they overlapped

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Hm, I think I remember having similar troubles with get_proper_types(). @Michael0x2a is this actually unsafe or maybe we can relax this somehow (I mean invariant generics in return types)?

return cast(List[Expression], self.translate_opt_expr_list(l))

def get_lineno(self, node: Union[ast3.expr, ast3.stmt]) -> int:
if (isinstance(node, (ast3.AsyncFunctionDef, ast3.ClassDef, ast3.FunctionDef))
and node.decorator_list):
Expand Down Expand Up @@ -988,7 +991,7 @@ def visit_IfExp(self, n: ast3.IfExp) -> ConditionalExpr:

# Dict(expr* keys, expr* values)
def visit_Dict(self, n: ast3.Dict) -> DictExpr:
e = DictExpr(list(zip(self.translate_expr_list(n.keys),
e = DictExpr(list(zip(self.translate_opt_expr_list(n.keys),
self.translate_expr_list(n.values))))
return self.set_line(e, n)

Expand Down