Requesting a data frame in Pandas Python

I have a problem requesting a dataframe in panda when I use a variable instead of a value.

df2 = pd.read_csv('my.csv')
query=df2.query('cc_vehicle_line==7')

      

        
        
        
      

    

works fine but

df2 = pd.read_csv('my.csv')
query=df2.query('cc_vehicle_line==variable_name')

      

        
        
        
      

    

It prints the message that variable_name is undefined. But it is defined. I cannot hardcoded the value, since I need to automate and depending on the value of variable_name, select the appropriate rows.

Did I miss something?

thank