Cannot declare method or static function parameter or return type as self of the class

[parsampsh]

BPO	42503
Nosy	@serhiy-storchaka, @iritkatriel, @parsampsh

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-11-29.14:35:04.921>
created_at = <Date 2020-11-29.12:58:55.359>
labels = ['3.8', 'type-bug', '3.7', '3.9', '3.10']
title = 'Cannot declare method or static function parameter or return type as self of the class'
updated_at = <Date 2020-11-29.14:35:04.919>
user = 'https://github.com/parsampsh'

bugs.python.org fields:

activity = <Date 2020-11-29.14:35:04.919>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2020-11-29.14:35:04.921>
closer = 'serhiy.storchaka'
components = []
creation = <Date 2020-11-29.12:58:55.359>
creator = 'parsampsh'
dependencies = []
files = []
hgrepos = []
issue_num = 42503
keywords = []
message_count = 3.0
messages = ['382061', '382064', '382066']
nosy_count = 3.0
nosy_names = ['serhiy.storchaka', 'iritkatriel', 'parsampsh']
pr_nums = []
priority = 'normal'
resolution = 'out of date'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42503'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10']

[parsampsh]

python raises error Undefined class X when you declaring parameter type or return type of method as the self of class:

class MyClass:
    def mymethod(self, a: MyClass): # parameter type is class self
        pass

# or

class MyClass:
    def mymethod(self) -> MyClass: # return type is class self
        pass
# or both of them

error Undefined class ... will be raised.

[iritkatriel]

Add at the top of your script:

from __future__ import annotations

[serhiy-storchaka]

You can already write such code in 3.10. In earlier Python versions you can either write annotation explicitly as string or (since 3.7) use and import suggested by Irit.