Возникает ошибка при компиляции SyntaxError: cannot assign to expression

import matplotlib.pyplot as plt
import numpy as np
import wave
import sys
import math
import contextlib
import librosa.display
from scipy.io import wavfile as wv
from scipy import signal as sg
from scipy.fftpack import fft
fname = 'PreEnd.wav'
outname = 'filtered.wav'
cutOffFrequency = 400.0
def running_mean(x, windowSize):
 cumsum = np.cumsum(np.insert(x, 0, 0))
 return (cumsum[windowSize:] - cumsum[:-windowSize]) / windowSize
def interpret_wav(raw_bytes, n_frames, n_channels, sample_width, interleaved =
True):
 if sample_width == 1:
    dtype = np.uint8
 elif sample_width == 2:
    dtype = np.int16
 else:
    raise ValueError("Only supports 8 and 16 bit audio formats.")
 channels = np.frombuffer(raw_bytes, dtype=dtype)
 if interleaved:
    channels.shape = (n_frames, n_channels)
    channels = channels.T
 else:
    channels.shape = (n_channels, n_frames)
 return channels
with contextlib.closing(wave.open(fname,'rb')) as spf:
 sampleRate = spf.getframerate()
 ampWidth = spf.getsampwidth()
 
 nChannels = spf.getnchannels()
 nFrames = spf.getnframes()
 signal = spf.readframes(nFrames*nChannels)
 spf.close()
 channels = interpret_wav(signal, nFrames, nChannels, ampWidth, True)
 freqRatio = (cutOffFrequency/sampleRate)
 N = int(math.sqrt(0.196196 + freqRatio**2)/freqRatio)
 l = x(n)-0.5*x(n-1) +0.5*x(n-2) = y(n)
 filtered = running_mean(channels[0], N).astype(channels.dtype)
 wav_file = wave.open(outname, "w")
 wav_file.setparams((1, ampWidth, sampleRate, nFrames, spf.getcomptype(),
spf.getcompname()))
 wav_file.writeframes(filtered.tobytes('C'))
 wav_file.close()
 f , rr = librosa.load(fname)
 plt.figure(figsize=(14, 5))
 librosa.display.waveplot(f, sr=rr)
 plt.show()
 x , sr = librosa.load(outname)
 plt.figure(figsize=(14, 5))
 librosa.display.waveplot(x, sr=sr)
 plt.show()

fname = 'PreEnd.wav'
wave.open(fname,'rb')
l = x(n)-0.5*x(n-1) +0.5*x(n-2) = y(n)