对python的isinstance的认识

>>> class objA:
...     pass
...
>>> A = objA()
>>> B = 'a','V'
>>> B
('a', 'V')
>>> C = 'a string'
>>> print instance(A,objA)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'instance' is not defined
>>> print isinstance(A,objA)
True
>>> print isinstance(B,tuple)
True
>>> print isinstance(C,tuple)
False
>>> print isinstance(C,string)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'string' is not defined
>>> print isinstance(C,basestring)
True
>>>