In the end, I wrote this: 
use Data::Structure::Util qw(get_refs utf8_on);

sub _perl_to_python_utf8_on {
    # We need to convert the hash keys ourselves.

    # 'get_refs' digs through the data structure
    # and returns an array ref of every reference
    # in the structure, at all levels.
    # All Hail CPAN; so glad I didn't have to walk
    # the data myself.
    my $refs = get_refs( $_[0] );

    # For each ref, process just the hashes.
    for my $ref ( @{$refs} ) {
        if ( ref($ref) eq 'HASH' ) {
            for my $key ( keys %$ref ) {
                # See text below.
                $ref->{ utf8_on($key) } = $ref->{$key};
            }
        }
    }

    # Let the utility convert everything else.
    return utf8_on( $_[0] );
}

[download]
You might think that the statement $ref->{ utf8_on($key) } = $ref->{$key}; would produce duplicate keys, but it does not; I went back and wrote key counting tests to prove it after reading other comments in this thread. The key (pun intended) to understanding what's going on here is that I believe utf8_on() only twiddles metadata; it does not change the actual value of the key. Hence we don't get duplicate entries and do not need to do 
$ref->{ utf8_on($key) } = delete $ref->{$key}.

[download]
You'd also think that I've now mismatched the key string and its metadata, but Inline::Python seems to be Doing the Right Thing with it, so I am leaving well enough alone for now. Maybe the utf8 'value' of each char is the same as its ascii value when less than 128 or 255?

In reply to Re: How to convert hash keys to utf8 by mpersico
in thread How to convert hash keys to utf8 by mpersico

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