code: def corr(self, col1, col2, method=None):
          
          if not isinstance(col1, basestring):
              raise ValueError("col1 should be a string.")
          if not isinstance(col2, basestring):
              raise ValueError("col2 should be a string.")
          if not method:
              method = "pearson"
          if not method == "pearson":
              raise ValueError("Currently only the calculation of the Pearson Correlation " +
                               "coefficient is supported.")
          return self._jdf.stat().corr(col1, col2, method)
docs: Calculates the correlation of two columns of a DataFrame as a double value.
          Currently only supports the Pearson Correlation Coefficient.
          :func:`DataFrame.corr` and :func:`DataFrameStatFunctions.corr` are aliases of each other.
  
          :param col1: The name of the first column
          :param col2: The name of the second column
          :param method: The correlation method. Currently only supports "pearson"