df2 = pd.DataFrame({ 'A' : 1.,
      'B' : pd.Timestamp('20130102'),
      'C' : pd.Series(1,index=list(range(4)),dtype='float32'),
      'D' : np.array([3] * 4,dtype='int32'),
      'E' : pd.Categorical(["test","train","test","train"]),
      'F' : 'foo' })
      
df2 值为：
    A          B   C D    E    F
0 1.0 2013-01-02 1.0 3 test  foo 
1 1.0 2013-01-02 1.0 3 train foo 
2 1.0 2013-01-02 1.0 3 test  foo 
3 1.0 2013-01-02 1.0 3 train foo

df2.dtypes：
A   float64
B   datetime64[ns]
C   float32
D   int32
E   category
F   object
dtype: object