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Allow instantiation of Type[A], if A is abstract#2853

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Merged
gvanrossum merged 7 commits intopython:masterfromilevkivskyi:abstract-type-ok
Mar 27, 2017
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@ilevkivskyi
ilevkivskyi committedMar 21, 2017
commit65eab95fdb766c43b94f466be31e50ed909d5cb2
5 changes: 3 additions & 2 deletionsmypy/checker.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -1151,14 +1151,15 @@ def check_assignment(self, lvalue: Lvalue, rvalue: Expression, infer_lvalue_type
else:
rvalue_type = self.check_simple_assignment(lvalue_type, rvalue, lvalue)

# Special case
# Special case: only non-abstract classes can be assigned to variables
# with explicit type Type[A].
if (
isinstance(rvalue_type, CallableType) and rvalue_type.is_type_obj() and
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I'm not keen on this formatting.

rvalue_type.type_object().is_abstract and
isinstance(lvalue_type, TypeType) and
isinstance(lvalue_type.item, Instance) and lvalue_type.item.type.is_abstract
):
self.fail("Cannot only assign non-abstract classes"
self.fail("Can only assign non-abstract classes"
" to a variable of type '{}'".format(lvalue_type), rvalue)
return
if rvalue_type and infer_lvalue_type:
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6 changes: 4 additions & 2 deletionsmypy/checkexpr.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -845,10 +845,12 @@ def check_arg(self, caller_type: Type, original_caller_type: Type,
messages.does_not_return_value(caller_type, context)
elif isinstance(caller_type, DeletedType):
messages.deleted_as_rvalue(caller_type, context)
# Only non-abstract classcould be given where Type[...] is expected
# Only non-abstract classcan be given where Type[...] is expected...
elif (isinstance(caller_type, CallableType) and isinstance(callee_type, TypeType) and
caller_type.is_type_obj() and caller_type.type_object().is_abstract and
isinstance(callee_type.item, Instance) and callee_type.item.type.is_abstract):
isinstance(callee_type.item, Instance) and callee_type.item.type.is_abstract and
# ...except for classmethod first argument
not caller_type.is_classmethod_class):
messages.fail("Only non-abstract class can be given where '{}' is expected"
.format(callee_type), context)
elif not is_subtype(caller_type, callee_type):
Expand Down
63 changes: 58 additions & 5 deletionstest-data/unit/check-abstract.test
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Expand Up@@ -157,8 +157,7 @@ class B(A): pass
B()# E: Cannot instantiate abstract class 'B' with abstract attributes 'f' and 'g'
[out]

[case testInstantiationAbstractsInType]
# flags: --python-version 3.6
[case testInstantiationAbstractsInTypeForFunctions]
from typing import Type
from abc import abstractmethod

Expand All@@ -172,26 +171,80 @@ class C(B):

def f(cls: Type[A]) -> A:
return cls() # OK

def g() -> A:
return A() # E: Cannot instantiate abstract class 'A' with abstract attribute 'm'

f(A) # E: Only non-abstract class can be given where 'Type[__main__.A]' is expected
f(B) # E: Only non-abstract class can be given where 'Type[__main__.A]' is expected
f(C) # OK
x: Type[B]
f(x) # OK
[out]

[case testInstantiationAbstractsInTypeForAliases]
from typing import Type
from abc import abstractmethod

class A:
@abstractmethod
def m(self) -> None: pass
class B(A): pass
class C(B):
def m(self) -> None:
pass

def f(cls: Type[A]) -> A:
return cls() # OK

Alias = A
GoodAlias = C
Alias() # E: Cannot instantiate abstract class 'A' with abstract attribute 'm'
GoodAlias()
f(Alias) # E: Only non-abstract class can be given where 'Type[__main__.A]' is expected
f(GoodAlias)
[out]

[case testInstantiationAbstractsInTypeForVariables]
from typing import Type
from abc import abstractmethod

class A:
@abstractmethod
def m(self) -> None: pass
class B(A): pass
class C(B):
def m(self) -> None:
pass

var: Type[A]
var()
var = A # E:Cannot only assign non-abstract classes to a variable of type 'Type[__main__.A]'
var = B # E:Cannot only assign non-abstract classes to a variable of type 'Type[__main__.A]'
var = A # E:Can only assign non-abstract classes to a variable of type 'Type[__main__.A]'
var = B # E:Can only assign non-abstract classes to a variable of type 'Type[__main__.A]'
var = C # OK

var_old = None # type: Type[A] # Old syntax for variable annotations
var_old()
var_old = A # E: Can only assign non-abstract classes to a variable of type 'Type[__main__.A]'
var_old = B # E: Can only assign non-abstract classes to a variable of type 'Type[__main__.A]'
var_old = C # OK
[out]

[case testInstantiationAbstractsInTypeForClassMethods]
from typing import Type
from abc import abstractmethod

class Logger:
@staticmethod
def log(a: Type[C]):
pass
class C:
@classmethod
def action(cls) -> None:
cls() #OK for classmethods
Logger.log(cls) #OK for classmethods
@abstractmethod
def m(self) -> None:
pass
[out]

[case testInstantiatingClassWithInheritedAbstractMethodAndSuppression]
Expand Down
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