Special case assignment to '_': always infer 'Any'

Fixes python#465
gvanrossum · Apr 16, 2018 · c87433d · c87433d
1 parent 6a8460f
commit c87433d
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diff --git a/mypy/checker.py b/mypy/checker.py
@@ -2016,6 +2016,10 @@ def infer_variable_type(self, name: Var, lvalue: Lvalue,
  # Make the type more general (strip away function names etc.).
  init_type = strip_type(init_type)
 
+ # Special case if target is named '_' -- the variable gets type Any.
+ if isinstance(lvalue, NameExpr) and lvalue.name == '_':
+ init_type = AnyType(TypeOfAny.special_form)
+
  self.set_inferred_type(name, lvalue, init_type)
 
  def infer_partial_type(self, name: Var, lvalue: Lvalue, init_type: Type) -> bool:

diff --git a/mypy/types.py b/mypy/types.py
@@ -281,6 +281,7 @@ class TypeOfAny(Enum):
  from_error = 'from_error'
  # Is this a type that can't be represented in mypy's type system? For instance, type of
  # call to NewType...). Even though these types aren't real Anys, we treat them as such.
+ # Also used for variables named '_'.
  special_form = 'special_form'
  # Does this Any come from interaction with another Any?
  from_another_any = 'from_another_any'