total_rows['ColumnID'] = total_rows['ColumnID'].astype(str)
df["fruit"] = df["fruit"].astype("|S")
# column names which need to be string
lst_str_cols = ['prefix', 'serial']
dict_dtypes = {x: 'str' for x in lst_str_cols}
pd.read_csv('sample.csv', dtype=dict_dtypes)