import numpy as np
  import matplotlib.pyplot as plt
  from scipy.fft import fft, ifft
  from scipy import signal
  
  t=np.arange(0,100,0.1)
  x= np.cos(2*np.pi*t)
  y= fft(x)
  
  
  p= np.linspace(0,1000,1,endpoint=True)
  u = signal.square( np.pi*5*p)
  e = np.fft.fft(u)
  plt.plot(p,e)