dataframe to dict such that one column is the key and the other is the value

df = pd.DataFrame([['p',1,3,2],['q',4,3,2],['r',4,0,9]], columns=['ID','A','B','C'])
df=df[['ID','A','B','C']]

df

  ID  A  B  C
0  p  1  3  2
1  q  4  3  2
2  r  4  0  9

your_dict = dict(zip(df.ID, df.B))

your_dict
 {'p': 3, 'q': 3, 'r': 0}

Something like this:

In [27]: df
Out[27]: 
  ID  A  B  C
0  p  1  3  2
1  q  4  3  2
2  r  4  0  9

In [30]: df.set_index('ID',inplace=True)
In [31]: df
Out[31]: 
    A  B  C
ID         
p   1  3  2
q   4  3  2
r   4  0  9

In [33]: df.to_dict()['B']
Out[33]: {'p': 3, 'q': 3, 'r': 0}