code: def fft_coefficient(self, x, param=None):
          
          if param is None:
              param = [{'attr': 'abs', 'coeff': 44}, {'attr': 'abs', 'coeff': 63}, {'attr': 'abs', 'coeff': 0},
                       {'attr': 'real', 'coeff': 0}, {'attr': 'real', 'coeff': 23}]
          _fft_coef = feature_calculators.fft_coefficient(x, param)
          logging.debug("fft coefficient by tsfresh calculated")
          return list(_fft_coef)
docs: As in tsfresh `fft_coefficient <https://github.com/blue-yonder/tsfresh/blob/master/tsfresh/feature_extraction/\
          feature_calculators.py#L852>`_ \
          Calculates the fourier coefficients of the one-dimensional discrete Fourier Transform for real input by fast \
          fourier transformation algorithm
          
          
          .. math:: 
          
              A_k =  \\sum_{m=0}^{n-1} a_m \\exp \\left \\{ -2 \\pi i \\frac{m k}{n} \\right \\}, \\qquad k = 0, \\ldots , n-1.
  
  
          The resulting coefficients will be complex, this feature calculator can return the real part (attr=="real"), \
          the imaginary part (attr=="imag), the absolute value (attr=""abs) and the angle in degrees (attr=="angle).
          
          :param x: the time series to calculate the feature of
          :type x: pandas.Series
          :param param: contains dictionaries {"coeff": x, "attr": s} with x int and x >= 0, s str and in ["real", "imag"\
          , "abs", "angle"]
          :type param: list
          :return: the different feature values
          :rtype: pandas.Series