> I would expect that this basic usage is very popular. If the file doesn't exist, the normal usage pattern fails in a confusing way: (...)

Well, the configparser is well defined. As you wrote: "If a file named in filenames cannot be opened, that file will be ignored."

You can check if the file exists or not by checking read() result:

"read(): (...) returning a list of filenames which were successfully parsed."
https://docs.python.org/dev/library/configparser.html#configparser.ConfigParser.read

I suggest to close this issue as "not a bug".

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For me, a better option would be to be able to pass an open file to configparser. So the caller can decide how to handle the open() error.