2.6 iat函数
与at的功能相同，只使用索引参数。
df.iat[3,0]
df.iat[3,'a']
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-22-e644c9fe0a65> in <module>
----> 1 df.iat[3,'a']
e:\anaconda3.5\lib\site-packages\pandas\core\indexing.py in __getitem__(self, key)
1783 raise ValueError('Invalid call for scalar access (getting)!')
-> 1785 key = self._convert_key(key)
1786 return self.obj.get_value(*key, takeable=self._takeable)
e:\anaconda3.5\lib\site-packages\pandas\core\indexing.py in _convert_key(self, key, is_setter)
1852 for a, i in zip(self.obj.axes, key):
1853 if not is_integer(i):
-> 1854 raise ValueError("iAt based indexing can only have integer "
1855 "indexers")
1856 return key
ValueError: iAt based indexing can only have integer indexers
