@property_cached<EOL><INDENT>def length_by_id(self):<DEDENT>
hashmap = dict((seq.id, len(seq)) for seq in self)<EOL>tmp = hashmap.copy()<EOL>hashmap.update(tmp)<EOL>return hashmap<EOL>
In some usecases you just need the sequence lengths in an indexed
        fashion. If you access this attribute, we will make a hash map in memory.