Different read_csv index_col = None / 0 / False in pandas-优快云博客

本文解释了如何使用Pandas库正确地从CSV文件中读取数据并设置索引列，包括不同参数如index_col的使用方法及其可能导致的误解。

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UPDATE

I think since version 0.16.1 it will now raise an error if you try to pass a boolean for index_col to avoid this ambiguity

ORIGINAL

A lot of people get confused by this, to specify the ordinal index of your column you should pass the int position in this case 0, what confuses people is that when there is no index column they pass False which is incorrect they should pass None. False will evaluate to 0 hence the result you observe.

In [3]:

import io
import pandas as pd
t="""index,a,b
0,hello,pandas"""
pd.read_csv(io.StringIO(t))

Out[3]:
   index      a       b
0      0  hello  pandas

The default value is index_col=None as shown above.

If we set index_col=0 we're explicitly stating to treat the first column as the index:

In [4]:

pd.read_csv(io.StringIO(t), index_col=0)
Out[4]:
           a       b
index               
0      hello  pandas

If we pass index_col=False we get the same result as above due to False evaluating to 0:

In [5]:

pd.read_csv(io.StringIO(t), index_col=False)
Out[5]:
   index      a       b
0      0  hello  pandas

If we now state index_col=None we get the same behaviour as when we didn't pass this param:

In [6]:

pd.read_csv(io.StringIO(t), index_col=None)
Out[6]:
   index      a       b
0      0  hello  pandas

EDIT

For the case where you have a blank index column which is what you have:

In [7]:

import io
import pandas as pd
t=""",a,b
0,hello,pandas"""
pd.read_csv(io.StringIO(t))

Out[7]:
   Unnamed: 0      a       b
0           0  hello  pandas
In [8]:

pd.read_csv(io.StringIO(t), index_col=0)
Out[8]:
       a       b
0  hello  pandas
In [9]:

pd.read_csv(io.StringIO(t), index_col=False)
Out[9]:
   Unnamed: 0      a       b
0           0  hello  pandas
In [10]:

pd.read_csv(io.StringIO(t), index_col=None)
Out[10]:
   Unnamed: 0      a       b
0           0  hello  pandas