Mypy forgets type information after a nested if-statement. #5378
Description
Mypy forgets type information after a nested if-statement. Small example:
class Base:
pass
class B(Base):
def __init__(self):
self.args = []
class C(Base):
def __init__(self):
self.args = []
def check(x: Base):
if isinstance(x, (B, C)):
print(x.args) # No error here.
if isinstance(x, B):
print("B")
elif isinstance(x, C):
print("C")
print(x.args) # error: "Base" has no attribute "args"
Mypy 0.620 correctly infers that x has a member args for the first print statement, but after the nested if statement, it has forgotten about that and throws an error.