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Treat underscore variables as anonymous #3125

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Treat underscore variables as anonymous #3125

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7c4910f
Support underscore vars
elazarg Apr 3, 2017
88a0437
Support underscore parameters
elazarg Apr 3, 2017
243094b
fix Python2 strangeness
elazarg Apr 3, 2017
a7b3d85
disallow multiple underscore params; test with and parameters
elazarg Apr 4, 2017
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8 changes: 5 additions & 3 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1566,12 +1566,14 @@ def check_lvalue(self, lvalue: Lvalue) -> Tuple[Type, IndexExpr, Var]:
elif isinstance(lvalue, IndexExpr):
index_lvalue = lvalue
elif isinstance(lvalue, MemberExpr):
lvalue_type = self.expr_checker.analyze_ordinary_member_access(lvalue,
True)
lvalue_type = self.expr_checker.analyze_ordinary_member_access(lvalue, True)
self.store_type(lvalue, lvalue_type)
elif isinstance(lvalue, NameExpr):
lvalue_type = self.expr_checker.analyze_ref_expr(lvalue, lvalue=True)
self.store_type(lvalue, lvalue_type)
if lvalue.name == '_':
lvalue_type = AnyType()
else:
self.store_type(lvalue, lvalue_type)
elif isinstance(lvalue, TupleExpr) or isinstance(lvalue, ListExpr):
types = [self.check_lvalue(sub_expr)[0] for sub_expr in lvalue.items]
lvalue_type = TupleType(types, self.named_type('builtins.tuple'))
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3 changes: 2 additions & 1 deletion mypy/semanal.py
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Expand Up @@ -3294,7 +3294,8 @@ def name_not_defined(self, name: str, ctx: Context) -> None:
self.fail(message, ctx)

def name_already_defined(self, name: str, ctx: Context) -> None:
self.fail("Name '{}' already defined".format(name), ctx)
if name != '_':
self.fail("Name '{}' already defined".format(name), ctx)

def fail(self, msg: str, ctx: Context, serious: bool = False, *,
blocker: bool = False) -> None:
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20 changes: 20 additions & 0 deletions test-data/unit/check-basic.test
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Expand Up @@ -261,6 +261,26 @@ main:3: error: Incompatible types in assignment (expression has type "B", variab
main:7: error: Incompatible types in assignment (expression has type "A", variable has type "B")
main:9: error: Incompatible types in assignment (expression has type "B", variable has type "A")

[case testUnderscoreVariableIsFresh]
from typing import Tuple
_ = 1
_ = ""
_ = "" # type: int
(_, _) = ("", 1.0 + "") # E: Unsupported left operand type for + ("float")
(_, _) = (1.0, "")
for (_, _) in ((1, "a"), (2, "b")): pass
(None for (_, _) in ((1, "a"), (2, "b")))

class A:
def __enter__(self) -> Tuple[int, str]: ...
def __exit__(self, *_) -> None: ...

with A() as (_, _): pass

def f(_: int) -> None:
_ = ""
_, _ = (1.0, b"")

[case testGlobalDefinedInBlockWithType]

class A: pass
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