I needed to have a simple FASTA file parser without using Biopython. There are just cases when you need to use some functions in Biopython but you can't install the whole package. In my case,  I wanted to handle and process sequences in FASTA format within a Google App Engine web app where it is not possible to install Python packages that have C extensions. Some of you may have other use cases, like when you want just the SeqIO.index() function to parse FASTA files. This is exactly what this short script tries to mimic. It has most of the methods and attributes of an indexed FASTA file using Bio.SeqIO in Biopython.

One of the routines in bioinformatics is fetching the sequence of a protein or DNA of a given accession number into either FASTA or Genbank format. I ran into the need of creating a short script that can do this for me and this is what I'm sharing here. It depends on modules from the Biopython package.

Whenever I need to accomplish something when I am programming, I first turn to Google to search if someone else already did something similar. Sometimes I am lucky to find complete working codes but sometimes I need to modify a bit. In either case, these are time-savers.  This is the motivation for my snippets post series. In simple terms, snippets are short re-usable codes.