Python class instance return value

My problem is as follows: I have a class Taskpane with a couple of methods. Instantiating works as it should. Now, when i show a list of all instantiated objects, i would like to print out a member variable per object for example the _tp_nr.

The following code returns the correct values, but it gets return in a strange(?) format.

This is the code:

#import weakref

class Taskpane():
    '''Taskpane class to hold all catalog taskpanes '''

    #'private' variables
    _tp_nr = ''
    _tp_title = ''
    _tp_component_name = ''

    #Static list for class instantiations
    _instances = []

    #Constructor
    def __init__(self, 
                  nr, 
                  title, 
                  component_name):

      self._tp_nr             = nr, 
      self._tp_title          = title, 
      self._tp_component_name = component_name

      #self.__class__._instances.append(weakref.proxy(self))
      self._instances.append(self)

    def __str__(self):
      return str( self._tp_nr )      

    def setTaskpaneId(self, value):
      self._tp_nr = value

    def getTaskpaneId(self):
      return str(self._tp_nr)

    def setTaskpaneTitle(self, value):
      self._tp_title = value

    def getTaskpaneTitle(self):
      return str(self._tp_title)

    def setTaskpaneComponentName(self, value):
      self._tp_component_name = value

    def getTaskpaneComponentName(self):
      return self._tp_component_name  

tp1 = Taskpane( '0', 'Title0', 'Component0' )
tp2 = Taskpane( '1', 'Title1', 'Component1' )

#print Taskpane._instances

#print tp1

for instance in Taskpane._instances:
    print( instance.getTaskpaneId() )

for instance in Taskpane._instances:
    print( instance.getTaskpaneTitle() ) 

Result:

('0',)
('1',)

('Title0',)
('Title1',)

The question is: Why does it return the results in this kind of formatting? I would expect only to see:

'0'
'1'

('Title0')
('Title1')

When using:

for instance in Taskpane._instances:
    print( instance._tp_nr )

The result is the same.