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  • [Python] RuntimeError: Invalid DISPLAY variable

    1.问题:在本地用matplotlib绘图可以,但是在ssh远程绘图的时候会报错 RuntimeError: Invalid DISPLAY variable

    2.原因:matplotlib的默认backend是TkAgg,而FltkAgg, GTK, GTKAgg, GTKCairo, TkAgg , Wx or WxAgg这几个backend都要求有GUI图形界面的,所以在ssh操作的时候会报错.

    import matplotlib.pyplot as plt
    Backend TkAgg is interactive backend. Turning interactive mode on.
    
    plt.get_backend()
    Out[3]: u'TkAgg'

    3.解决方法:指定不需要GUI的backend(Agg, Cairo, PS, PDF or SVG

    import matplotlib.pyplot as plt
    plt.switch_backend('agg')

    4.源码

    查看plt.switch_backend()的源码实现和解析:

    def switch_backend(newbackend):
        """
        Switch the default backend.  This feature is **experimental**, and
        is only expected to work switching to an image backend.  e.g., if
        you have a bunch of PostScript scripts that you want to run from
        an interactive ipython session, you may want to switch to the PS
        backend before running them to avoid having a bunch of GUI windows
        popup.  If you try to interactively switch from one GUI backend to
        another, you will explode.
    
        Calling this command will close all open windows.
        """
        close('all')
        global _backend_mod, new_figure_manager, draw_if_interactive, _show
        matplotlib.use(newbackend, warn=False, force=True)
        from matplotlib.backends import pylab_setup
        _backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()

    查看matplotlib.use()的源码:

    def use(arg, warn=True, force=False):
        """
        Set the matplotlib backend to one of the known backends.
    
        The argument is case-insensitive. *warn* specifies whether a
        warning should be issued if a backend has already been set up.
        *force* is an **experimental** flag that tells matplotlib to
        attempt to initialize a new backend by reloading the backend
        module.
    
        .. note::
    
            This function must be called *before* importing pyplot for
            the first time; or, if you are not using pyplot, it must be called
            before importing matplotlib.backends.  If warn is True, a warning
            is issued if you try and call this after pylab or pyplot have been
            loaded.  In certain black magic use cases, e.g.
            :func:`pyplot.switch_backend`, we are doing the reloading necessary to
            make the backend switch work (in some cases, e.g., pure image
            backends) so one can set warn=False to suppress the warnings.
    
        To find out which backend is currently set, see
        :func:`matplotlib.get_backend`.
    
        """
        # Lets determine the proper backend name first
        if arg.startswith('module://'):
            name = arg
        else:
            # Lowercase only non-module backend names (modules are case-sensitive)
            arg = arg.lower()
            name = validate_backend(arg)
    
        # Check if we've already set up a backend
        if 'matplotlib.backends' in sys.modules:
            # Warn only if called with a different name
            if (rcParams['backend'] != name) and warn:
                warnings.warn(_use_error_msg)
    
            # Unless we've been told to force it, just return
            if not force:
                return
            need_reload = True
        else:
            need_reload = False
    
        # Store the backend name
        rcParams['backend'] = name
    
        # If needed we reload here because a lot of setup code is triggered on
        # module import. See backends/__init__.py for more detail.
        if need_reload:
            reload(sys.modules['matplotlib.backends'])

    参考:DISPLAY error matplotlib http://chewpichai.blogspot.com/2008/01/display-error-matplotlib.html 。原文可能被墙了,需要设法翻一下。

    原文内容:

    DISPLAY error matplotlib
    When error occur about this "$DISPLAY not set" when you run python code that use matplotlib this happened because your matplotlib backend is set to FltkAgg, GTK, GTKAgg, GTKCairo, TkAgg , Wx or WxAgg they required a GUI that why error occur.
    
    To solve this you must specific other backend that not required GUI (Agg, Cairo, PS, PDF or SVG) when use matplotlib like this 
    
    In code
    import matplotlib matplotlib.use('Agg')
    In command line use
    -d option python subplot_demo.py -dAgg Remember when call savefig('filename') don't give it extension this will handle by backend that you specific e.g Agg will create file filename.png
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  • 原文地址:https://www.cnblogs.com/bymo/p/7447409.html
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