ImportError: Matplotlib qt-based backends require an external PyQt4, PyQt5

>>> import matplotlib.pyplot as plt

当运行上面的简单import语句时，出现了下面的错误：

Traceback (most recent calllast):

File "<stdin>",line 1, in <module>

File"/usr/local/lib/python2.7/dist-packages/matplotlib/pyplot.py",line 115, in <module>

_backend_mod,new_figure_manager, draw_if_interactive, _show = pylab_setup()

File"/usr/local/lib/python2.7/dist-packages/matplotlib/backends/__init__.py",line 32, in pylab_setup

globals(),locals(),[backend_name],0)

File"/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_qt4agg.py",line 18, in <module>

from .backend_qt5agg importFigureCanvasQTAggBase as _FigureCanvasQTAggBase

File"/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_qt5agg.py",line 16, in <module>

from .backend_qt5 importQtCore

File"/usr/local/lib/python2.7/dist-packages/matplotlib/backends/backend_qt5.py",line 26, in <module>

importmatplotlib.backends.qt_editor.figureoptions as figureoptions

File"/usr/local/lib/python2.7/dist-packages/matplotlib/backends/qt_editor/figureoptions.py",line 20, in <module>

importmatplotlib.backends.qt_editor.formlayout as formlayout

File"/usr/local/lib/python2.7/dist-packages/matplotlib/backends/qt_editor/formlayout.py",line 56, in <module>

frommatplotlib.backends.qt_compat import QtGui, QtWidgets, QtCore

File"/usr/local/lib/python2.7/dist-packages/matplotlib/backends/qt_compat.py",line 179, in <module>

"Matplotlib qt-basedbackends require an external PyQt4, PyQt5,\n"

ImportError:Matplotlib qt-based backends require an external PyQt4, PyQt5,

or PySide package to beinstalled, but it was not found.

只要import  matplotlib.pyplot 就会出现这种错误，以前没有出现过，按错误提示去install PySide时又出现别的问题，查

了查，像是因为装QT5引起的，Ubuntu16.04系统自带的是QT4，我装完QT5后发现/usr/lib/x86_64-linux-gnu/qt4/bin

下面没有可执行文件了，无奈只能把QT4再安装一下了

(1) 安装QT4

username@machine:~$ sudo apt-get install build-essential

username@machine:~$ sudo apt-get install qt4-dev-tools qt4-doc qt4-qtconfig qt4-demosqt4-designer

(2) 安装PySide

username@machine:~$ sudo pip install PySide -i https://pypi.tuna.tsinghua.edu.cn/simple #-i后面是一个镜像

使用下面的方法也可以解决上面的问题，只是多了一两行代码

>>> import matplotlib

>>> matplotlib.use(“Agg”)      # 或着matplotlib.use(“GTK”)或者matplotlib.use(“Qt5Agg”)

>>> importmatplotlib.pyplot as plt

matplotlib.use()用来指定matplotlib用哪个backend

matplotlib.get_backend()可以查看matplotlib当前用的backend是哪个

/usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf这个链接文件可以查看当前使用哪个版本的QT