最近我下载了pyqtgraph模块。我在解压缩文件夹后运行构建并安装，但是当我运行一个简单的示例（如此处）时
import pyqtgraph as pg
import numpy as np
x = np.random.normal(size=1000)
y = np.random.normal(size=1000)
pg.plot(x, y, pen=None, symbol='o') ## setting pen=None disables line drawing
我收到一个错误：
Traceback (most recent call last):
File "main.py", line 1, in <module>
import pyqtgraph as pg
ImportError: No module named pyqtgraph
我在ubuntu 14.04上运行，并且pyqtgraph在/usr/local/lib/python2.7/dist-packages下。有人可以帮助我吗？