Where I work, many of our users are involved in bioinformatics and recently one user was concerned with the time it took to convert an aligned FASTA file into an interleaved PHYLIP file for phylogenetic analysis. Using BioPython took a very long time and not to mention its in memory representation was many times larger then the actual file itself and this added to the difficulties the user was facing.
So I thought I could help out. Luckily an existing project existed, pyfasta. This great tool uses Numpy’s mmap to access a fasta file without having to read it completely into memory and then with some loops, I was able to convert to the phylip format. I’m also happy to report that the user is very satisfied with this program.