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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 copy_out(source: Iterable[bytes], dest: io.BytesIO, use_placeholders: bool = False):
 """ Copy lines from source to destination. :param source: Source line iterable. :param dest: Destination open file. :param use_placeholders: When true, convert lines containing placeholders to empty lines and drop true empty lines (assume to be spuriously generated). """

    for line in source:
        if use_placeholders:
            # True empty lines are assumed to be spurious as the placeholder
            # should be passed through
            if not line.strip():
                continue
            if line.startswith(PLACEHOLDER):
                line = b"\n"
        dest.write(line)