import pandas as pd
import numpy as np
a = np.arange(12).reshape(3,4)
print a
>
[[ 0 1 2 3]
 [ 4 5 6 7]
 [ 8 9 10 11]]
df = pd.DataFrame(a)
print df
>
 0 1 2 3
0 0 1 2 3
1 4 5 6 7
2 8 9 10 11
print df.loc[0]
>
0 0
1 1
2 2
3 3
Name: 0, dtype: int32
print df.iloc[0]
0 0
1 1
2 2
3 3
Name: 0, dtype: int32
print df.loc[:,[0,3]]
 0 3
0 0 3
1 4 7
2 8 11
print df.iloc[:,[0,3]]
 0 3
0 0 3
1 4 7
2 8 11

df.index = ['a','b','c'] 
print df 
> 
 0 1 2 3 
a 0 1 2 3 
b 4 5 6 7 
c 8 9 10 11 
print df.loc[0] 
# TypeError: cannot do label indexing on <class 'pandas.core.indexes.base.Index'> with these indexers [0] of <type 'int'> 
print df.iloc[0] 
> 
0 0 
1 1 
2 2 
3 3 
Name: a, dtype: int32 
print df.iloc['a'] # TypeError: cannot do positional indexing on <class 'pandas.core.indexes.base.Index'> with these indexers [a] of <type 'str'> 
print df.loc['a'] # 正确 
> 
0 0 
1 1 
2 2 
3 3 
Name: a, dtype: int32 

df.columns = ['A','B','C','D']
print df
>
 A B C D
a 0 1 2 3
b 4 5 6 7
c 8 9 10 11
print df.loc[:,'A']
>
a 0
b 4
c 8
Name: A, dtype: int32
print df.iloc[:,'A'] # ValueError: Location based indexing can only have [integer, integer slice (START point is INCLUDED, END point is EXCLUDED), listlike of integers, boolean array] types

print df.ix[0]
>
A 0
B 1
C 2
D 3
Name: a, dtype: int32
print df.ix['a']
>
A 0
B 1
C 2
D 3
Name: a, dtype: int32
print df.ix[:,0]
>
a 0
b 4
c 8
Name: A, dtype: int32
print df.ix[:,'A']
>
a 0
b 4
c 8
Name: A, dtype: int32