iloc cannot enlarge its target object

　　在使用pandas过程中，你可能遇见iloc cannot enlarge its target object这个问题，这个错误提示你df或者series的索引超出了范围，要解决该问题其实很简单。

　　我们先复现一下这个问题：

　　1、试图给1个series新增元素赋值。

# -*- coding:UTF-8 -*-
import pandas as pd

series = pd.Series([1,2,3])
series.iloc[3] = 4
print(series)

Traceback (most recent call last):
  File "D:/py3script/pandas_xuexi/pandas_test.py", line 5, in 
    series.iloc[3] = 4
  File "D:\python3\install\lib\site-packages\pandas\core\indexing.py", line 667, in __setitem__
    self._has_valid_setitem_indexer(key)
  File "D:\python3\install\lib\site-packages\pandas\core\indexing.py", line 1394, in _has_valid_setitem_indexer
    raise IndexError("iloc cannot enlarge its target object")
IndexError: iloc cannot enlarge its target object

　　2、试图给1个df新增1行赋值。

# -*- coding:UTF-8 -*-
import pandas as pd

df = pd.DataFrame([[1, 2], [4, 5], [7, 8]],
     index=['x', 'y', 'z'],
     columns=['max_speed', 'shield'])

df.iloc[3] = 4
print(df)

Traceback (most recent call last):
  File "D:/py3script/pandas_xuexi/pandas_test.py", line 8, in 
    df.iloc[3] = 4
  File "D:\python3\install\lib\site-packages\pandas\core\indexing.py", line 667, in __setitem__
    self._has_valid_setitem_indexer(key)
  File "D:\python3\install\lib\site-packages\pandas\core\indexing.py", line 1394, in _has_valid_setitem_indexer
    raise IndexError("iloc cannot enlarge its target object")
IndexError: iloc cannot enlarge its target object

　　如果series或者df中以新增元素的方式赋值，那么应该使用loc来实现。代码如下：

# -*- coding:UTF-8 -*-
import pandas as pd

df = pd.DataFrame([[1, 2], [4, 5], [7, 8]],
     index=['x', 'y', 'z'],
     columns=['max_speed', 'shield'])

df.loc[4] = 4
print(df)

   max_speed  shield
x          1       2
y          4       5
z          7       8
4          4       4

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