如何在python中分别读取csv文件的两个字段？

Question

I want to read two column of a csv file separately, but when I wrote code like below python just show first column and nothing for second, but in the csv file the second column also has lots of rows.

import csv
import pprint

f = open("arachnid.csv", 'r')
read = csv.DictReader(f)
for i in range(3):
    read.next()

for i in read:
    pprint.pprint(i["binomialAuthority_label"])

for i in read:
    pprint.pprint(i["rdf-schema#label"])

Answer 1

The reason for this is that when you use DictReader the way you are using it it will create what is called an iterator/generator. So, when you have iterated over it once, you cannot iterate over it again the way you are doing it.

If you want to keep your logic as is, you can actually call seek(0) on your file reader object to reset its position as such:

f.seek(0)

The next time you iterate over your dictreader object, it will give you what you are looking for. So the part of your code of interest would be this:

for i in read:
    pprint.pprint(i["binomialAuthority_label"])

# This is where you set your seek(0) before the second loop
f.seek(0)

for i in read:
    pprint.pprint(i['rdf-schema#label'])

Answer 2

Your DictReader instance gets exhausted after your first for i in read: loop, so when you try to do your second loop, there is nothing to iterate over.

What you want to do, once you've iterated over the CSV the first time, you can seek your file back to the start, and create a new instance of the DictReader and start again. You'll want to create a new DictReader instance otherwise you'll need to manually skip the header line.

f = open(filename)
read = csv.DictReader(f)
for i in read:
    print i

f.seek(0)
read = csv.DictReader(f)
for i in read:
    print i