>>> keyvalue = ('cat', 'dog')
>>> cboCombo = ttk.Combobox(root, values=keyvalue, width=68)
>>> value = cboCombo.get()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'get'
The same error is also generated for its current() method.