执行FFT后对应于特定频率的幅度

Question

输入信号以特定频率到达。我正在对此进行FFT，然后想要找到与该特定频率相对应的幅度。我不确定我是否朝着正确的方向前进？以下是我提出的两个功能：

def fft_v2(y, freq, fs=30000):
    Ts = 1.0/fs; # sampling interval
    t = np.arange(0,1,Ts) # time vector

    n = len(y) # length of the signal
    k = np.arange(n)
    T = n/fs
    frequency = k/T # two sides frequency range
    frequency = frequency[range(n/2)] # one side frequency range

    Y = np.fft.fft(y)/n # fft computing and normalization
    Y = Y[range(n/2)]

    amplitude = []

    for fq,amp in zip(frequency, Y):
        if fq == freq:
            amplitude.append(max(abs(Y)))

    print max(amplitude)


def fft(y, freq, fs=30000):
    n  = len(y)      # Get the signal length
    dt = 1/float(fs) # Get time resolution

    fft_output = np.fft.rfft(y)     # Perform real fft
    rfreqs = np.fft.rfftfreq(n, dt) # Calculatel frequency bins
    fft_mag = np.abs(fft_output)    # Take only magnitude of spectrum

    # Normalize the amplitude by number of bins and multiply by 2
    # because we removed second half of spectrum above the Nyqist 
    # frequency and energy must be preserved   
    fft_mag = fft_mag * 2 / n           

    print np.array(fft_mag), np.array(rfreqs) 

在第二个函数中，如何找到对应于特定频率的幅度？