Editing Biopython (section)

=== Input and output ===
Biopython can read and write to a number of common sequence formats, including [[FASTA format|FASTA]], [[FASTQ format|FASTQ]], GenBank, Clustal, PHYLIP and [[Nexus file|NEXUS]].  When reading files, descriptive information in the file is used to populate the members of Biopython classes, such as <code>SeqRecord</code>.  This allows records of one file format to be converted into others.

Very large sequence files can exceed a computer's memory resources, so Biopython provides various options for accessing records in large files.  They can be loaded entirely into memory in Python data structures, such as lists or [[Associative array|dictionaries]], providing fast access at the cost of memory usage.  Alternatively, the files can be read from disk as needed, with slower performance but lower memory requirements.

<syntaxhighlight lang="pycon">
>>> # This script loads a file containing multiple sequences and saves each one in a different format.
>>> from Bio import SeqIO
>>> genomes = SeqIO.parse("salmonella.gb", "genbank")
>>> for genome in genomes:
...     SeqIO.write(genome, genome.id + ".fasta", "fasta")
</syntaxhighlight>