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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 dataframe(self):
 """Build and cache a dataframe from query results"""


        if self._dataframe is None:
            try:
                import pandas as pd
            except ImportError:
                raise RuntimeError('To enable dataframe support, '
                                   'run \'pip install datadotworld[pandas]\'')

            self._dataframe = pd.DataFrame.from_records(self._iter_rows(),
                                                        coerce_float=True)

        return self._dataframe