python - matplotlib 图从 QT 抛出 TypeError

Question

问题

当我运行时

import matplotlib.pyplot as plt
plt.plot([1,2,3,4])

我收到错误

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "[...]/lib/python3.5/site-packages/matplotlib/pyplot.py", line 1203, in subplots
    fig = figure(**fig_kw)
  File "[...]/lib/python3.5/site-packages/matplotlib/pyplot.py", line 535, in figure
    **kwargs)
  File "[...]/lib/python3.5/site-packages/matplotlib/backends/backend_qt4agg.py", line 46, in new_figure_manager
    return new_figure_manager_given_figure(num, thisFig)
  File "[...]/lib/python3.5/site-packages/matplotlib/backends/backend_qt4agg.py", line 53, in new_figure_manager_given_figure
    canvas = FigureCanvasQTAgg(figure)
  File "[...]/lib/python3.5/site-packages/matplotlib/backends/backend_qt4agg.py", line 76, in __init__
    FigureCanvasQT.__init__(self, figure)
  File "[...]/lib/python3.5/site-packages/matplotlib/backends/backend_qt4.py", line 66, in __init__
    QtWidgets.QWidget.__init__(self)
TypeError: __init__() missing 1 required positional argument: 'figure'

这种方法直到最近才有效。我不知道我更改了已安装的 anaconda 库中的任何内容，这些库当前(仅显示相关库):

matplotlib                2.0.0               np111py35_0    conda-forge
qt                        5.6.2                         3    defaults
qtconsole                 4.2.1                    py35_1    defaults

我需要做什么才能解决这个问题？

更多信息

当导入matplotlib时我得到

Backend Qt4Agg is interactive backend. Turning interactive mode on.
Failed to enable GUI event loop integration for 'qt4'
Traceback (most recent call last):
  File "[...]/PyCharm/pycharm-community-2016.3.2/helpers/pydev/_pydev_bundle/pydev_console_utils.py", line 563, in do_enable_gui
    enable_gui(guiname)
  File "[...]/PyCharm/pycharm-community-2016.3.2/helpers/pydev/pydev_ipython/inputhook.py", line 528, in enable_gui
    return gui_hook(app)
  File "[...]/PyCharm/pycharm-community-2016.3.2/helpers/pydev/pydev_ipython/inputhook.py", line 195, in enable_qt4
    from pydev_ipython.inputhookqt4 import create_inputhook_qt4
  File "[...]/PyCharm/pycharm-community-2016.3.2/helpers/pydev/_pydev_bundle/pydev_import_hook.py", line 21, in do_import
    module = self._system_import(name, *args, **kwargs)
  File "[...]/PyCharm/pycharm-community-2016.3.2/helpers/pydev/pydev_ipython/inputhookqt4.py", line 25, in <module>
    from pydev_ipython.qt_for_kernel import QtCore, QtGui
  File "[...]/PyCharm/pycharm-community-2016.3.2/helpers/pydev/_pydev_bundle/pydev_import_hook.py", line 21, in do_import
    module = self._system_import(name, *args, **kwargs)
  File "[...]/PyCharm/pycharm-community-2016.3.2/helpers/pydev/pydev_ipython/qt_for_kernel.py", line 85, in <module>
    QtCore, QtGui, QtSvg, QT_API = load_qt(api_opts)
  File "[...]/PyCharm/pycharm-community-2016.3.2/helpers/pydev/pydev_ipython/qt_loaders.py", line 281, in load_qt
    api_options))
ImportError: 
    Could not load requested Qt binding. Please ensure that
    PyQt4 >= 4.7 or PySide >= 1.0.3 is available,
    and only one is imported per session.
    Currently-imported Qt library:   None
    PyQt4 installed:                 False
    PyQt5 installed:                 True
    PySide >= 1.0.3 installed:       True
    Tried to load:                   ['pyqtdefault']

当我使用 python script.py 运行脚本时，我没有收到上述消息，而是得到了

[...]/lib/python3.5/site-packages/matplotlib/__init__.py:1401: UserWarning:  This call to matplotlib.use() has no effect
because the backend has already been chosen;
matplotlib.use() must be called *before* pylab, matplotlib.pyplot,
or matplotlib.backends is imported for the first time.

Answer 1

我猜测发生了类似以下的事情，尽管我不能确定，因为没有给出有关两种情况的确切代码。

当您(无意中)尝试使用未安装的后端时，可能会出现第一个错误。

import matplotlib #everthing works fine, no backend selected yet
matplotlib.use("TkAgg") #backend selected, would still be fine even if Tk wasnt installed.
import matplotlib.pyplot as plt # backend registered. Still not used.
plt.plot(..)  # now the backend will be used. Clash! 
              # Backend cannot be used, since underlying library is missing

后来您尝试使用不同的后端。

import matplotlib #everthing works fine, no backend selected yet
matplotlib.use("TkAgg") #backend selected, would still be fine even if Tk wasnt installed.
import matplotlib.pyplot as plt # backend registered. Still not used.
....
import matplotlib
matplotlib.use("Qt5Agg") # backend "TkAgg" has already been registered. 
                         # You cannot change it anymore.

这就是你的目标

This call to matplotlib.use() has no effect because the backend has already been chosen; matplotlib.use() must be called before pylab, matplotlib.pyplot, or matplotlib.backends is imported for the first time.

解决方案:

如果您需要使用特定后端，请始终遵循此顺序。

1. 导入matplotlib
2. matplotlib.use("TkAgg")
3. 将 matplotlib.pyplot 导入为 plt
4. 绘图，例如plt.plot(..)

如果您不需要特定的后端(大多数情况下都是这种情况)，请让 matplotlib 决定选择哪一个 - 省略步骤 1 和 2!。特别是在共享代码时，您甚至无法确定所需后端的库是否安装在其他用户的系统上。