human
Solve the following python programming problem given the following code:
def test_modify(self) : 
    mh = getMH () 
    eq = self.assertEquals 
    mh.makefolder ('dummy1') 
    self.assert_ (('dummy1' in mh.listfolders ())) 
    path = os.path.join (_mhpath, 'dummy1') 
    self.assert_ (os.path.exists (path)) 
    f = mh.openfolder ('dummy1') 
    def create(n) : 
        msg = ('From: foo
Subject: %s

Dummy Message %s
' % (n, n)) 
        f.createmessage (n, StringIO.StringIO (msg)) 
create (7) 
    create (8) 
    create (9) 
    eq (readFile (f.getmessagefilename (9)), 'From: foo
Subject: 9

Dummy Message 9
') 
    eq (f.listmessages (), [7, 8, 9]) 
    files = os.listdir (path) 
    files.sort () 
    eq (files, ['7', '8', '9']) 
    f.removemessages (['7', '8']) 
    files = os.listdir (path) 
    files.sort () 
    eq (files, [',7', ',8', '9']) 
    eq (f.listmessages (), [9]) 
    create (10) 
    create (11) 
    create (12) 
    mh.makefolder ('dummy2') 
    f2 = mh.openfolder ('dummy2') 
    eq (f2.listmessages (), []) 
    f.movemessage (10, f2, 3) 
    f.movemessage (11, f2, 5) 
    eq (f.listmessages (), [9, 12]) 
    eq (f2.listmessages (), [3, 5]) 
    eq (readFile (f2.getmessagefilename (3)), 'From: foo
Subject: 10

Dummy Message 10
') 
    f.copymessage (9, mh, 4) 
    eq (f.listmessages (), [9, 12]) 
    eq (readFile (f2.getmessagefilename (4)), 'From: foo
Subject: 9

Dummy Message 9
') 
    f.refilemessages ([9, 12], f2) 
    eq (f.listmessages (), []) 
    eq (f2.listmessages (), [3, 4, 5, 6, 7]) 
    eq (readFile (f2.getmessagefilename (7)), 'From: foo
Subject: 12

Dummy Message 12
') 
    mh.deletefolder ('dummy1') 
    mh.deletefolder ('dummy2') 
    self.assert_ (('dummy1' not in mh.listfolders ())) 
    self.assert_ ((not os.path.exists (path))) 

    
    

    Fix the buggy line: f.copymessage (9, mh, 4)
assistant
#Here is Python code to fix the buggy line: f.

f.copymessage (9, f2, 4)