[New-bugs-announce] [issue41086] Exception for uninstantiated interpolation (configparser)

[Brian Faherty]

New submission from Brian Faherty <anothergenericuser at gmail.com>:

The ConfigParser in Lib has a parameter called `interpolation`, that expects an instance of a subclass of Interpolation. However, when ConfigParser is given an argument of an uninstantiated subclass of Interpolation, the __init__ function of ConfigParser accepts it and continues on. This results in a later receiving an error message along the lines of `TypeError: before_set()
missing 1 required positional argument: 'value'` when functions are later called on the ConfigParser instance. This delay between the feedback and the original mistake has led to a few bugs open on the issue tracker (https://bugs.python.org/issue26831 and https://bugs.python.org/issue26469. Both of which were closed after a quick and simple explanation, which can be easily implemented in the library itself. 

I've created a PR for this work and will attach it shortly. Please let me know if there is a better name for the exception other than `InterpolationIsNotInstantiatedError`. It seems long, but also in line with the other Errors already in configparser.

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components: Library (Lib)
messages: 372137
nosy: Brian Faherty
priority: normal
severity: normal
status: open
title: Exception for uninstantiated interpolation (configparser)
type: behavior
versions: Python 3.10, Python 3.5, Python 3.6, Python 3.7, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41086>
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