为什么两个“ for循环”都不起作用？

Question

import csv

def csv_reader(file_obj):      
    reader = csv.reader(file_obj)
    # for row in reader:
        # print(" ".join(row))

    reader_2 = csv.DictReader(file_obj, delimiter=",")
    for row_2 in reader_2:
        print(row_2)

csv_path = "data.csv"
with open(csv_path, "r") as f_obj:
    csv_reader(f_obj)

I can't figure out why the second "for loop" only prints any text if the first "for loop" is commented out.

Answer 1

The CSV reader has already consumed your file. Calling file_obj.seek(0) before using it again should do the trick.

Alternatively, opening (and then closing) the file for each operation will also work.

Answer 2

It's because you are passing the same file handler to both csv reader objects. Once you iterate over it once, you have to manually do file_obj.seek(0) for it to work as intended, or else it simply acts like an empty file.