[issue30888] import class not isinstance of the class

[邱伟略]

New submission from 邱伟略:

the working directory is like below:

bug/
    dirc/
        __init__.py
        foo.py
        foo2.py
    __init__.py
    foo1.py
    

in foo.py:
```
class Event(object):
    pass
```

in foo2.py:
```
from a.foo import Event

def fun():
    return Event()
```

in foo1.py:
```
from bug.a.foo import Event
from bug.a.foo2 import fun

assert isinstance(fun(), Event)
```

when i try to execute the code in foo1.py, i got an assertion error.

but if i change foo2.py to:
```
from ..a.foo import Event

def fun():
    return Event()

```

the code in foo1.py can be done well without the assertion error.

i think it's about the import mechanism. 

i have checked pep328

I think 
when i do "from a.foo import Event", python import Event by the package name "a.foo.Event", but "from ..a.foo import Event" is going to import Event by "bug.a.foo.Event". and it is totally different in python.

is it kind of bug python should prevent?

----------
components: macOS
messages: 298018
nosy: ned.deily, ronaldoussoren, 邱伟略
priority: normal
severity: normal
status: open
title: import class not isinstance of the class
type: behavior
versions: Python 3.6

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue30888>
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