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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 _list_samples(self, predicate=None):
 """List all samples that meet the predicate or all if predicate is not specified. Args: predicate: Match samples against this predicate (or all if not specified) Returns: List of the md5s for the matching samples """

        cursor = self.database[self.sample_collection].find(predicate, {'_id':0, 'md5':1})
        return [item['md5'] for item in cursor]