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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 digest_packets(packets, hasher):
 """Compute digest on specified packets, according to '_to_hash' field."""

    data_to_hash = io.BytesIO()
    for p in packets:
        data_to_hash.write(p['_to_hash'])
    hasher.update(data_to_hash.getvalue())
    return hasher.digest()