[Python] RuntimeError: Invalid DISPLAY variable

標籤：image   war   lod   pos   pdf   black   pen   creat   ant   

１．問題：在本地用matplotlib繪圖可以，但是在ssh遠程繪圖的時候會報錯　RuntimeError: Invalid DISPLAY variable

２．原因：matplotlib的預設backend是TkAgg，而FltkAgg, GTK, GTKAgg, GTKCairo, TkAgg , Wx or WxAgg這幾個backend都要求有GUI圖形介面的，所以在ssh操作的時候會報錯．

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

３．解決方案：指定不需要GUI的backend（Agg, Cairo, PS, PDF or SVG）

import matplotlib.pyplot as pltplt.switch_backend(‘agg‘)

４．源碼

查看plt.switch_backend()的源碼實現和解析：

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()的源碼：

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‘])

 

參考：DISPLAY error matplotlib　http://chewpichai.blogspot.com/2008/01/display-error-matplotlib.html 。原文可能被牆了，需要設法翻一下。

原文內容：

DISPLAY error matplotlibWhen 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 optionpython subplot_demo.py -dAggRemember 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

 

[Python] RuntimeError: Invalid DISPLAY variable