df_asset['Dwell_Type']=df_asset['Dwell_Type'].astype('O')#here we used uppercase O to set as object.
df_asset['Zone_Class']=df_asset['Zone_Class'].astype('O')
df_asset['OverallQual']=df_asset['OverallQual'].astype('O')
df_asset['OverallCond']=df_asset['OverallCond'].astype('O')
df_asset['BsmtFullBath']=df_asset['BsmtFullBath'].astype('O')
df_asset['BsmtHalfBath']=df_asset['BsmtHalfBath'].astype('O')