numpy - 属性错误: 'numpy.ndarray' object has no attribute '_hold'

Question

我在Python3中使用numpy和matplotlib。
以下代码导致错误:

import matplotlib
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure
from matplotlib.axes import Subplot as plt
from matplotlib import pylab


 a=[1,1]
 b=[1,1]
 fsam = 48000         
 w, h = freqz(b, a, worN=2000)
 plt.plot(((fsam-8000) * 0.5 / np.pi) * w, abs(h), label=" ")   

matplotlib 1.3.x 的实际错误:

 File "/usr/local/lib/python3.2/dist-packages/matplotlib-1.3.x-py3.2-linux-x86_64.egg/matplotlib/axes.py", line 4119, in plot   
     if not self._hold:   
AttributeError: 'numpy.ndarray' object has no attribute '_hold'   

matplotlib 1.2.0 的实际错误:

 Traceback (most recent call last):   
   File "/home/christoph/audio_measurement/AudioTools/AudioTools.py", line 222, in <module>   
       main()   
     File "/home/christoph/audio_measurement/AudioTools/AudioTools.py", line 216, in main   
       form = AppForm()   
     File "/home/christoph/audio_measurement/AudioTools/AudioTools.py", line 39, in __init__   
       self.on_draw()   
     File "/home/christoph/audio_measurement/AudioTools/AudioTools.py", line 80, in on_draw   
       self.transfer = Transfer(self.canvas)   
     File "/home/christoph/audio_measurement/AudioTools/Transfer.py", line 42, in __init__   
       plt.plot(((fsam-8000) * 0.5 / np.pi) * w, abs(h), label=" ")   
     File "/usr/local/lib/python3.2/dist-packages/matplotlib/axes.py", line 3995, in plot   
       if not self._hold: self.cla()   
AttributeError: 'numpy.ndarray' object has no attribute '_hold'   

Transfer 是一个类，它绘制在 Canvas 上。

我查看了系数a和b的长度，但它们并没有影响结果。
我找不到任何相关内容。有谁知道出了什么问题吗？

Answer 1

通常我会使用 import matplotlib.pyplot as plt 和 plt.plot、plt.subplot、plt.show 等——甚至只是 from pylab import *。无论如何，这一行

from matplotlib.axes import Subplot as plt

是您有一个未绑定(bind)的 plot 函数尝试对 ndarray 参数进行操作的原因。 Subplot 需要实例化。这应该有效:

import numpy as np
from scipy.signal import freqz

import matplotlib
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure
from matplotlib.axes import Subplot

fig = Figure()
ax = Subplot(fig, 111)
fig.add_subplot(ax)
canvas = FigureCanvas(fig)

a=[1,1]
b=[1,1]
fsam = 48000         
w, h = freqz(b, a, worN=2000)

ax.plot(((fsam-8000) * 0.5 / np.pi) * w, abs(h), label=" ")
canvas.show()