Repository navigation
Type of the same class inside the class #3661
Description
I have a method that returns itself but it doesn't know the type of the class inside
class TcpFlow(object):
def __init__(self) -> None:
self.matches = [] # type: List[str]
def __enter__(self) -> TcpFlow:
return selfI got this error
Traceback (most recent call last):
File "example/sample.py", line 2, in <module>
from tcpflow import TcpFlow
File "/Users/mrkaspa/code/py/tcpflow.py/tcpflow/__init__.py", line 1, in <module>
from .tcpflow import TcpFlow
File "/Users/mrkaspa/code/py/tcpflow.py/tcpflow/tcpflow.py", line 8, in <module>
class TcpFlow(object):
File "/Users/mrkaspa/code/py/tcpflow.py/tcpflow/tcpflow.py", line 16, in TcpFlow
def __enter__(self) -> TcpFlow:
NameError: name 'TcpFlow' is not defined
Reacted by Alexander Regueiro, Leo Gallucci, Danilo Batista de Queiroz, Felipe S. S. Schneider, Pranithan and Genaro Camele
Activity
ilevkivskyi commentedon Jul 5, 2017
In such cases you should put the name of class in quotes (this is called forward reference), like this:
Garrett-R commentedon Jun 23, 2020
As of Python 3.7, you can now do:
(notice the quotes around the return type have been removed)
johnthagen commentedon Dec 15, 2022
As of Python 3.11, you can now use the
Selftype to express the intent clearly and concisely:This new pattern can be applied to previous versions of Python using
typing_extensions.Selfbackport.Note that this removed the need to use:
which is important as the SC has tentatively accepted PEP 649, which indicates the future will be to move away from
from __future__ import annotations.