<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def parse(cls, fptr, offset, length):
 """Parse component definition box. Parameters fptr : file Open file object. offset : int Start position of box in bytes. length : int Length of the box in bytes. Returns ------- ComponentDefinitionBox Instance of the current component definition box. """

        num_bytes = offset + length - fptr.tell()
        read_buffer = fptr.read(num_bytes)

        # Read the number of components.
        num_components, = struct.unpack_from('>H', read_buffer)

        data = struct.unpack_from('>' + 'HHH' * num_components, read_buffer,
                                  offset=2)
        index = data[0:num_components * 6:3]
        channel_type = data[1:num_components * 6:3]
        association = data[2:num_components * 6:3]

        return cls(index=tuple(index),
                   channel_type=tuple(channel_type),
                   association=tuple(association),
                   length=length, offset=offset)