FAQ: Learn Python: Files - Reading Different Types of CSV Files

This community-built FAQ covers the “Reading Different Types of CSV Files” exercise from the lesson “Learn Python: Files”.

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This exercise can be found in the following Codecademy content:

Learn Python 3

FAQs on the exercise Reading Different Types of CSV Files

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1 Like

7 posts were split to a new topic: Do I need to use @ or a , for the delimiter?

12 posts were split to a new topic: Understanding the newline argument

20 posts were split to a new topic: Python Files Lesson Code Submission Errors

4 posts were split to a new topic: How can I use append with each?

2 posts were split to a new topic: Responses to deleted message

Hi all,

Thank you again for reading this.

My question is about the “newline = ‘’” argument. I understand what the intention behind using that line is. I just don’t understand the mechanism behind its action. What’s between the ‘’ marks exactly?

Thank you again.

Hello all,

Thank you for reading this.

My question is about CSV files and the way we “extract” certain values from it. From the examples I’ve seen so far, it seems like the CSV files have columns (for example ‘name,’ ‘address,’ etc.). Then why is it that when we’re iterating through cvs.DictReader instance, we use the term “row” instead?

having columns doesn’t mean there are no rows

you can iterate through whatever you want, you, the programmer, are the one deciding what happens in your program

have you looked at a csv file? what would iterating through that mean? maybe you can answer your own question if you consider what’s being done instead of how it’s done

and if you iterate through a csv file that you have looked at, what do you get, do you get columns, or rows, and what would you therefore say it is?

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Thank you for your response. I think I got it.

Currently finishing up the section and I understand the solution they gave but while working on my own I can’t figure out the line of code I would need to combine the lists outputs after the for loop iterations

import csv

with open("books.csv") as books_csv:
  books_reader = csv.DictReader(books_csv, delimiter="@")
  for book in books_reader:
    isbn_list = []
1 Like

Create the empty list before the for loop, that is the only error in your code.


Here is(are) my solution(s).
I wanted to write this as a list comprehension to begin with but couldn’t quite wrap my head around the logic.
So instead I wrote a for loop first, and then reading the for loop backwards wrote the list comprehension.

First solution is commented out, list comprehension follows that.

with open('books.csv') as books_csv:
  books_reader = csv.DictReader(books_csv, delimiter='@')
  #isbn_list = []
  #for book in books_reader:
  #  isbn_list.append(book['ISBN'])
  isbn_list = [isbn_list.append(book['ISBN']) for book in books_reader]

Nice - I’m kinda surprised that works though as you are both assigning to and appending to isbn_list at the same time. The comprehension defines the new list so you can skip the append step altogether.

All you need for that last line is:

isbn_list = [book['ISBN'] for book in books_reader]
1 Like

I don’t understand this line:

isbn_list = [book['ISBN'] for book in books_reader]

I understand that is a ‘shorter’ way to append the ISBN more directly but Can someone explain step by step?


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Have you completed the list section that describes comprehensions?

First, let’s look at it in imperative form (instruction steps):

isbn_list = []
for book in books_reader:

From the above we need to assume the makeup of books_reader and book objects. The syntax suggests, book is a dictionary (dict) and books_reader is a list.

The loop takes one object off the list and appends the value of its ISBN attribute to the ISBN list. That is our objective, build a list of ISBNs from the data store.

You should be comfortable with this. Give us a thumbs up and we can go on…

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Oh my, I completely forgot the comprehension syntax. I understand now. Thank you,

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I do have a slightly different question when talking about csv files. What is the difference between the following code:

isbn_list = [book[“ISBN”] for book in books_reader]

isbn_list =
for book in books_reader:
isbn_list += book[“ISBN”]

Both of these codes look identical. The top one is a list comprehension vs, the bottom one is a list iteration. The bottom one iterates each and every character in books_reader. Why does it do that?? Maybe I am answering my own question, but I just need some clarification.

The above is the same as list.extend() which extends a list with another list. Wrap square brackets around the object in the assignment:

list += [object]

Question about the scope of the with statement.

import csv

with open("demo.csv") as demo_csv:
  csv_reader = csv.DictReader(demo_csv, delimiter = ",")
  names = []
  for row in csv_reader:

I thought that the scope of a code indentation limits a variable to the block and discards it for the outside.
Is this not the case for with () statments or why does print(names) work even outside the with statement, here?