Global name is not defined

ERROR:  Traceback (most recent call last):
   File "main.py", line 139, in <module>
     PlanLekcji().run()
   File "/usr/lib/python2.7/dist-packages/kivy/app.py", line 766, in run
     root = self.build()
   File "main.py", line 125, in build
     sm.add_widget(BellsScreen(name='bells'))
 TypeError: __init__() got an unexpected keyword argument 'name'


class BellsScreen(Screen):

    def __init__(self):
        self.skrocone = False

    def toogle_skrocone(self,nr):
        nr = int(nr)
        if skrocone == True:
            skrocone = False
        else:
            skrocone = True
        if nr == 0:
            root.show_bells()
        else:
            root.show_breaks()

    def show_bells(self):
        if skrocone==True:
            file = open("Info/Bells2.txt","rb")
        else:
            file = open("Info/Bells1.txt","rb")
        data = file.read()
        file.close()
        self.ids.dzwonki_label.text = data
        return data

    pass