psytrans.py separates the sequences of a host species from those of its main symbiont(s) or parasite(s) based on Support Vector Machine classification. The program takes as input a file in fasta format with the sequences to be classified. The program also requires a file with sequences of a species related to the host, and a file with sequences related to the symbiont (or parasite). The queries will be compared to these two files using BLASTX. Alternatively, the user can provide the output of pre-computed BLASTX searches (in tabular format: -outfmt 6 or 7). The classification is then carried out using the command line tools from libsvm.