def _edit(self, filename, line=None):
        """ Opens a Python script for editing.

        Parameters:
        -----------
        filename : str
            A path to a local system file.

        line : int, optional
            A line of interest in the file.
        """
        if self.custom_edit:
            self.custom_edit_requested.emit(filename, line)
        elif not self.editor:
            self._append_plain_text('No default editor available.\n'
            'Specify a GUI text editor in the `IPythonWidget.editor` '
            'configurable to enable the %edit magic')
        else:
            try:
                filename = '"%s"' % filename
                if line and self.editor_line:
                    command = self.editor_line.format(filename=filename,
                                                      line=line)
                else:
                    try:
                        command = self.editor.format()
                    except __HOLE__:
                        command = self.editor.format(filename=filename)
                    else:
                        command += ' ' + filename
            except KeyError:
                self._append_plain_text('Invalid editor command.\n')
            else:
                try:
                    Popen(command, shell=True)
                except OSError:
                    msg = 'Opening editor with command "%s" failed.\n'
                    self._append_plain_text(msg % command)
dataset/ETHPy150Open ipython/ipython-py3k/IPython/frontend/qt/console/ipython_widget.py/IPythonWidget._edit