code: def _zeropad(sig, N, axis=0):
      
      # ensures concatenation dimension is the first
      sig = np.moveaxis(sig, axis, 0)
      # zero pad
      out = np.zeros((sig.shape[0] + N,) + sig.shape[1:])
      out[:sig.shape[0], ...] = sig
      # put back axis in place
      out = np.moveaxis(out, 0, axis)
      return out
docs: pads with N zeros at the end of the signal, along given axis