def get_N50(readlengths):
return readlengths[np.where(np.cumsum(readlengths) >= <NUM_LIT:0.5> * np.sum(readlengths))[<NUM_LIT:0>][<NUM_LIT:0>]]<EOL>
Calculate read length N50.

    Based on https://github.com/PapenfussLab/Mungo/blob/master/bin/fasta_stats.py