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Add support for tuple values on except clauses #1610

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52 changes: 22 additions & 30 deletions mypy/checker.py
Original file line number Diff line number Diff line change
Expand Up @@ -1782,7 +1782,7 @@ def visit_try_stmt(self, s: TryStmt) -> Type:
for i in range(len(s.handlers)):
self.binder.push_frame()
if s.types[i]:
t = self.exception_type(s.types[i])
t = self.visit_except_handler_test(s.types[i])
if s.vars[i]:
# To support local variables, we make this a definition line,
# causing assignment to set the variable's type.
Expand Down Expand Up @@ -1822,38 +1822,30 @@ def visit_try_stmt(self, s: TryStmt) -> Type:
if s.finally_body:
self.accept(s.finally_body)

def exception_type(self, n: Node) -> Type:
if isinstance(n, TupleExpr):
t = None # type: Type
for item in n.items:
tt = self.exception_type(item)
if t:
t = join_types(t, tt)
else:
t = tt
return t
else:
# A single exception type; should evaluate to a type object type.
type = self.accept(n)
return self.check_exception_type(type, n)
self.fail('Unsupported exception', n)
return AnyType()
def visit_except_handler_test(self, n: Node) -> Type:
"""Type check an exception handler test clause."""
type = self.accept(n)
if isinstance(type, AnyType):
return type

def check_exception_type(self, type: Type, context: Context) -> Type:
if isinstance(type, FunctionLike):
item = type.items()[0]
ret = item.ret_type
if (is_subtype(ret, self.named_type('builtins.BaseException'))
all_types = [] # type: List[Type]
test_types = type.items if isinstance(type, TupleType) else [type]

for ttype in test_types:
if not isinstance(ttype, FunctionLike):
self.fail(messages.INVALID_EXCEPTION_TYPE, n)
return AnyType()

item = ttype.items()[0]
ret_type = item.ret_type
if not (is_subtype(ret_type, self.named_type('builtins.BaseException'))
and item.is_type_obj()):
return ret
else:
self.fail(messages.INVALID_EXCEPTION_TYPE, context)
self.fail(messages.INVALID_EXCEPTION_TYPE, n)
return AnyType()
elif isinstance(type, AnyType):
return AnyType()
else:
self.fail(messages.INVALID_EXCEPTION_TYPE, context)
return AnyType()

all_types.append(ret_type)

return UnionType.make_simplified_union(all_types)

def visit_for_stmt(self, s: ForStmt) -> Type:
"""Type check a for statement."""
Expand Down
51 changes: 51 additions & 0 deletions mypy/test/data/check-statements.test
Original file line number Diff line number Diff line change
Expand Up @@ -573,6 +573,24 @@ except (E1, E2) as e1:
except (E2, E1) as e2:
a = e2 # type: E1
b = e2 # type: E2 # E: Incompatible types in assignment (expression has type "E1", variable has type "E2")
except (E1, E2, int) as e3: # E: Exception type must be derived from BaseException
pass
[builtins fixtures/exception.py]

[case testExceptWithMultipleTypes3]
import typing
class E1(BaseException): pass
class E1_1(E1): pass
class E1_2(E1): pass
try: pass
except (E1, E1_1, E1_2) as e1:
x = e1 # type: E1
y = e1 # type: E1_1 # E: Incompatible types in assignment (expression has type "E1", variable has type "E1_1")
z = e1 # type: E1_2 # E: Incompatible types in assignment (expression has type "E1", variable has type "E1_2")
except (E1_1, E1_2) as e2:
a = e2 # type: E1
b = e2 # type: E1_1 # E: Incompatible types in assignment (expression has type "Union[E1_1, E1_2]", variable has type "E1_1")
c = e2 # type: E1_2 # E: Incompatible types in assignment (expression has type "Union[E1_1, E1_2]", variable has type "E1_2")
[builtins fixtures/exception.py]

[case testReuseTryExceptionVariable]
Expand Down Expand Up @@ -618,6 +636,39 @@ except exc as e: pass # E: Exception type must be derived from BaseE
except BaseException() as b: pass # E: Exception type must be derived from BaseException
[builtins fixtures/exception.py]

[case testTupleValueAsExceptionType]
import typing
def exc() -> BaseException: pass
class E1(BaseException): pass
class E1_1(E1): pass
class E1_2(E1): pass

exs1 = (E1, E1_1, E1_2)
try: pass
except exs1 as e1:
x = e1 # type: E1
y = e1 # type: E1_1 # E: Incompatible types in assignment (expression has type "E1", variable has type "E1_1")
z = e1 # type: E1_2 # E: Incompatible types in assignment (expression has type "E1", variable has type "E1_2")

exs2 = (E1_1, E1_2)
try: pass
except exs2 as e2:
a = e2 # type: E1
b = e2 # type: E1_1 # E: Incompatible types in assignment (expression has type "Union[E1_1, E1_2]", variable has type "E1_1")
c = e2 # type: E1_2 # E: Incompatible types in assignment (expression has type "Union[E1_1, E1_2]", variable has type "E1_2")
[builtins fixtures/exception.py]

[case testInvalidTupleValueAsExceptionType]
import typing
def exc() -> BaseException: pass
class E1(BaseException): pass
class E2(E1): pass

exs1 = (E1, E2, int)
try: pass
except exs1 as e: pass # E: Exception type must be derived from BaseException
[builtins fixtures/exception.py]

[case testOverloadedExceptionType]
from typing import overload
class E(BaseException):
Expand Down