pycompat: extract function that converts attribute or encoding name to str This will be used to convert encoding.encoding to a str acceptable by Python 3 functions. The source encoding is changed to "latin-1" because encoding.encoding can have arbitrary bytes. Since valid names should consist of ASCII characters, we don't care about the mapping of non-ASCII characters so long as invalid names are distinct from valid names.

Added signature for changeset 149433e68974

pycompat: provide 'ispy3' constant We compare version_info at several places, which seems enough to define a constant.