When mentioning the constants contained in the module email.charset, the documentation prefixes them with "Charset", for example: Charset.QP, Charset.BASE64, Charset.SHORTEST. This suggests that the constants can be found on the class "Charset" (uppercase first letter) in the module, while they are in fact contained in the the "charset" (lowercase first letter) module itself.

This is probably a left-over from when the module was called email.Charset (in 2.2 I believe). Under Python 2.7, while the documentation uses the same nomenclature, at least the module is also importable under the name email.Charset so it makes more sense.