While working on `tox-ini-fmt`, a formatter for - you guessed it - `tox.ini` files, I noticed ConfigParser strips comments when reading a config file.

( https://github.com/tox-dev/tox-ini-fmt/issues/34 )

While reasonable, this behaviour is surprising, as it is neither documented at https://docs.python.org/3/library/configparser.html nor in the docstrings (read and _read) which I read at first.

The stripping of comments is only documented with inline comments

https://github.com/jugmac00/cpython/blob/610a60c601fb4380eee30e15be1cd4dcbdaeec4c/Lib/configparser.py#L1019

and

https://github.com/jugmac00/cpython/blob/610a60c601fb4380eee30e15be1cd4dcbdaeec4c/Lib/configparser.py#L1031

Once I found these comments, I was surprised once again, as in my code the inline comments were not stripped. After some more pdb-ing and reading the source of ConfigParser, I noticed that - while comments have a default value, inline comments do not - and that is why when you read a config file, some comments get removed and others not.

I'd like to work on a pull request to document this behaviour, both in the official documentation and in the docstrings of the read and the _read methods.