Bug in ConfigParser when setting new values in extended interpolation

[MichaelJacob]

BPO	26469
Nosy	@ambv

^{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 2016-03-02.09:53:47.923>
created_at = <Date 2016-03-02.09:40:40.534>
labels = ['invalid', 'library', 'type-crash']
title = 'Bug in ConfigParser when setting new values in extended interpolation'
updated_at = <Date 2022-02-17.12:22:51.625>
user = 'https://bugs.python.org/MichaelJacob'

bugs.python.org fields:

activity = <Date 2022-02-17.12:22:51.625>
actor = 'lukasz.langa'
assignee = 'none'
closed = True
closed_date = <Date 2016-03-02.09:53:47.923>
closer = 'Michael Jacob'
components = ['Library (Lib)']
creation = <Date 2016-03-02.09:40:40.534>
creator = 'Michael Jacob'
dependencies = []
files = []
hgrepos = []
issue_num = 26469
keywords = []
message_count = 3.0
messages = ['261101', '261102', '413400']
nosy_count = 2.0
nosy_names = ['lukasz.langa', 'Michael Jacob']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue26469'
versions = ['Python 3.5']

[MichaelJacob]

There seems to be a bug in configparser when setting new values in extended interpolation:

python --version
Python 3.5.1

from configparser import ConfigParser, ExtendedInterpolation
c=ConfigParser(interpolation=ExtendedInterpolation)
c.add_section('test')
c.set('test', 'key', 'value')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.5/configparser.py", line 1190, in set
    super().set(section, option, value)
  File "/usr/lib/python3.5/configparser.py", line 891, in set
    value)
TypeError: before_set() missing 1 required positional argument: 'value'

It works ithout extended interpolation, though.

[MichaelJacob]

My bad.

ConfigParser expects an interpolation object, not a class.

Instead of c=ConfigParser(interpolation=ExtendedInterpolation)

you need to create it with:

c=ConfigParser(interpolation=ExtendedInterpolation())

Sorry about that.

[ambv]

Note: the problem here was due to passing ExtendedInterpolation (the class) instead of ExtendedInterpolation() (the object). This is now fixed through BPO-41086.