为什么我的 Python CSV 代码在每一行中都以字符串形式读取？

Question

I'm working on a spin-off project from a Code Academy lesson and running into an error when trying to append a specific column from each row of a CSV to a list.

The code from the lesson :

import csv

with open('cool_csv.csv') as cool_csv_file:
  cool_csv_dict = csv.DictReader(cool_csv_file)
  for row in cool_csv_dict:
    print(row['Cool Fact'])

I need to read in each row from my CSV, and append the value of the "subject" column to the entries list.

import csv

entries = []

with open("list.csv") as list_csv:
  list_reader = csv.DictReader(list_csv)
  for row in list_csv:
    entries.append(row["subject"])

But I'm getting the following error:

entries.append(row[“subject”]) TypeError: string indices must be integers

I get that the error is saying that the value passed by row was a string, so I can't access it with the header name, but what I don't get is why. My file is a valid CSV as far as I can see, and my code is no different to that in the lesson other than appending instead of printing (I tested print, same error.)

My CSV:

subject,subject_type
first,test
second,test

What have I done wrong that's making my code read in a string instead of the csv row?

Answer 1

You need to loop the reader

  for row in list_csv:
      entries.append(row["subject"])

You are looping the list_csv by mistake.

Answer 2

as @AlirezaTajadod was saying, you are iterating over a bad object, you have to iterate over list_reader

with open("list.csv") as list_csv:
  list_reader = csv.DictReader(list_csv)
  for row in list_reader:
    entries.append(row["subject"])

Answer 3

Need to use list_reader instead of list_csv . See the following example file, marks.csv .

id,subject,marks
1,English,20
2,French,21
3,Spanish,21

So we have,

import csv
list_reader = csv.DictReader(open("marks.csv"))

You may iterate over the rows of the CSV file by iterating over list_reader . So if we do a for loop like below

for row in list_reader:
    print row

It will print row like this,

{'id': '1', 'subject': 'English','marks': '20' }
{'id': '2', 'subject': 'French', 'marks': '21' }
{'id': '3', 'subject': 'Spanish','marks': '22' }

Now to get the subject value simply do print row['subject']