These are the unblessed Perl basic types:

!!perl/hash     # hash reference
!!perl/array    # array reference
!!perl/scalar   # scalar reference
!!perl/code     # code reference
!!perl/io       # io reference
!!perl/glob     # a glob (not a ref)
!!perl/regexp   # a regexp (not a ref)
!!perl/ref      # a container ref to any of the above

All of the above types can be blessed:

!!perl/hash:Foo::Bar   # hash ref blessed with 'Foo::Bar'
!!perl/glob:Foo::Bar   # glob blessed with 'Foo::Bar'
etc...

There could be a form that requires there to be a class in memory to handle it. If there is no Foo::Bar class, an exception is thrown.

!!perl/object:Foo::Bar  # object type is determined by Foo::Bar

These blessed forms could be shortened to:

!!perl/:Foo.Bar   # Foo::Bar hash (can't use % in urls)
!!perl/@Foo.Bar   # Foo::Bar array
!!perl/$Foo.Bar   # Foo::Bar scalar
!!perl/&Foo.Bar   # Foo::Bar code
!!perl/+Foo.Bar   # Foo::Bar io
!!perl/*Foo.Bar   # Foo::Bar glob
!!perl/\Foo.Bar   # Foo::Bar reference
!!perl/Foo.Bar    # Foo::Bar object

The '!!perl' forms are only consumable by Perl. To share objects with Python, maybe use this form:

!!object:Foo.Bar