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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 Select, Add, Delete, Columns
Step1:  dictionary like operations
dictionary selection with string index
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Python Code:
import pandas as pd
import numpy as np
Explanation: Select, Add, Delete, Columns
End of explanation
cookbook_df = pd.DataFrame({'AAA' : [4,5,6,7], 'BBB' : [10,20,30,40],'CCC' : [100,50,-30,-50]})
cookbook_df['BBB']
Explanation: dictionary like operations
dictionary selection with string index
End of explanation
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