def find_identifier(self):
features = self.data['<STR_LIT>']<EOL>n = len(features)<EOL>feature = features[<NUM_LIT:0>]<EOL>if '<STR_LIT:id>' in feature and len(set(feat['<STR_LIT:id>'] for feat in features)) == n:<EOL><INDENT>return '<STR_LIT>'<EOL><DEDENT>for key in feature.get('<STR_LIT>', []):<EOL><INDENT>if len(set(feat['<STR_LIT>'][key] for feat in features)) == n:<EOL><INDENT>return '<STR_LIT>'.format(key)<EOL><DEDENT><DEDENT>if self.embed:<EOL><INDENT>for i, feature in enumerate(self.data['<STR_LIT>']):<EOL><INDENT>feature['<STR_LIT:id>'] = str(i)<EOL><DEDENT>return '<STR_LIT>'<EOL><DEDENT>raise ValueError(<EOL>'<STR_LIT>'<EOL>'<STR_LIT>'<EOL>'<STR_LIT>'<EOL>)<EOL>
Find a unique identifier for each feature, create it if needed.