Check if x server is running

    Returns
    -------
    system_supports_plotting : bool
        True when on Linux and running an xserver.  Returns None when
        on a non-linux platform.

def system_supports_plotting():
    """
    Check if x server is running

    Returns
    -------
    system_supports_plotting : bool
        True when on Linux and running an xserver.  Returns None when
        on a non-linux platform.

    """
    try:
        if os.environ['ALLOW_PLOTTING'].lower() == 'true':
            return True
    except KeyError:
        pass
    try:
        p = Popen(["xset", "-q"], stdout=PIPE, stderr=PIPE)
        p.communicate()
        return p.returncode == 0
    except:
        return False