from jcvi.apps.base import OptionParser, set_outfile parser = OptionParser() parser.add_option("-o", "--output", dest="output_file", default="output.txt", help="write output to FILE") (options, args) = parser.parse_args() out_file = set_outfile(options.output_file) out_file.write("Hello, world!")In this example, we create an option parser with an option `-o` that specifies the output file. We then use `set_outfile` to ensure that the output is written to the specified file (or `output.txt` by default). Finally, we write the string "Hello, world!" to the output file. This example uses the `jcvi` library, which is a bioinformatics toolkit for Python. The `jcvi.apps.base` module provides basic utilities for command line applications in the `jcvi` framework.