You could provide a list of columns to be dropped and return back the dataframeDataFrame with only the columns needed using the drop()drop() function on a pandas dataframePandas DataFrame.
Just saying
colsToDrop = ['a']
df.drop(colsToDrop, axis=1)
colsToDrop = ['a']
df.drop(colsToDrop, axis=1)
would return a dataframeDataFrame with just the columns bb and cc.
The drop method is documented http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.drop.htmlhere.