from scipy.fftpack import fft
import numpy as np

x = np.array([1, 2, 3, 4])

x

array([1, 2, 3, 4])

y = fft(x)

y

array([10.+0.j, -2.+2.j, -2.+0.j, -2.-2.j])

import matplotlib.pyplot as plt

plt.plot(x, y, 'ro')
plt.axis([-5, 20, -5, 20])
plt.show()

/Users/rajacsp/anaconda3/envs/py36/lib/python3.6/site-packages/numpy/core/numeric.py:538: ComplexWarning: Casting complex values to real discards the imaginary part
  return array(a, dtype, copy=False, order=order)