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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 populateFromHeader(self, readGroupHeader):
 """ Populate the instance variables using the specified SAM header. """

        self._sampleName = readGroupHeader.get('SM', None)
        self._description = readGroupHeader.get('DS', None)
        if 'PI' in readGroupHeader:
            self._predictedInsertSize = int(readGroupHeader['PI'])
        self._instrumentModel = readGroupHeader.get('PL', None)
        self._sequencingCenter = readGroupHeader.get('CN', None)
        self._experimentDescription = readGroupHeader.get('DS', None)
        self._library = readGroupHeader.get('LB', None)
        self._platformUnit = readGroupHeader.get('PU', None)
        self._runTime = readGroupHeader.get('DT', None)