python script
root = "..." commit_info = svncl.propset( "myprop", "Test", root, revision=pysvn.Revision(pysvn.opt_revision_kind.head))
shows an error, pysvn._pysvn_2_7.ClientError: The path "..." does not exist in version 0.
You need to set base_revision_for_url:
commit_info = svncl.propset( "myprop", "Test", root, base_revision_for_url=svncl.revpropget("revision", root)[0].number )
See this bug report for reference: http://pysvn.tigris.org/issues/show_bug.cgi?id=146