Add instancemethod to types.py

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-02-08.05:36:55.534>
labels = ['3.8', 'type-feature', 'library']
title = 'Add instancemethod to types.py'
updated_at = <Date 2019-02-08.13:06:52.129>
user = 'https://github.com/mr-nfamous'

bugs.python.org fields:

activity = <Date 2019-02-08.13:06:52.129>
actor = 'cheryl.sabella'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-02-08.05:36:55.534>
creator = 'bup'
dependencies = []
files = []
hgrepos = []
issue_num = 35937
keywords = []
message_count = 4.0
messages = ['335058', '335072', '335074', '335077']
nosy_count = 4.0
nosy_names = ['ronaldoussoren', 'steven.daprano', 'bup', 'cheryl.sabella']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue35937'
versions = ['Python 3.8']