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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def depends(func):
 """ Decorator to perform check on infile and outfile. When infile is not present, issue warning, and when outfile is present, skip function calls. """

    from jcvi.apps.base import need_update, listify

    infile = "infile"
    outfile = "outfile"

    def wrapper(*args, **kwargs):
        assert outfile in kwargs, \
            "You need to specify `outfile=` on function call"
        if infile in kwargs:
            infilename = listify(kwargs[infile])
            for x in infilename:
                assert op.exists(x), \
                    "The specified infile `{0}` does not exist".format(x)

        outfilename = kwargs[outfile]
        if need_update(infilename, outfilename):
            return func(*args, **kwargs)
        else:
            msg = "File `{0}` exists. Computation skipped." \
                .format(outfilename)
            logging.debug(msg)

        outfilename = listify(outfilename)

        for x in outfilename:
            assert op.exists(x), \
                "Something went wrong, `{0}` not found".format(x)

        return outfilename

    return wrapper