How to append from file into list in Python?

Question

I have a sample file called 'scores.txt' which holds the following values:

10,0,6,3,7,4

I want to be able to somehow take each value from the line, and append it to a list so that it becomes sampleList = [10,0,6,3,7,4].

I have tried doing this using the following code below,

score_list = []

opener = open('scores.txt','r')

for i in opener:
    score_list.append(i)

print (score_list)

which partially works, but for some reason, it doesn't do it properly. It just sticks all the values into one index instead of separate indexes. How can I make it so all the values get put into their own separate index?

You have a list, not an array. The latter is something different in Python. — Martijn Pieters
– Martijn Pieters, Commented Jan 23, 2016 at 16:44

Martijn Pieters · Accepted Answer · 2016-01-23 16:58:07Z

3

You have CSV data (comma separated). Easiest is to use the csv module:

import csv

all_values = []

with open('scores.txt', newline='') as infile:
    reader = csv.reader(infile)
    for row in reader:
        all_values.extend(row)

Otherwise, split the values. Each line you read is a string with the ',' character between the digits:

all_values = []

with open('scores.txt', newline='') as infile:
    for line in infile:
        all_values.extend(line.strip().split(','))

Either way, all_values ends up with a list of strings. If all your values are only consisting of digits, you could convert these to integers:

all_values.extend(map(int, row))

or

all_values.extend(map(int, line.strip().split(',')))

edited Jan 23, 2016 at 16:58

answered Jan 23, 2016 at 16:47

Martijn Pieters

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2 Comments

Gabriel A. Over a year ago

Using the first solution that you provided gives me a Line 13 in reader = csv(infile): TypeError: 'module' object is not callable error. Do you know why that may be?

Martijn Pieters Over a year ago

@TeeKayM: because I'm a numpty and forgot the .reader part.

desa · Accepted Answer · 2016-01-23 16:50:40Z

3

That is an efficient way how to do that without using any external package:

with open('tmp.txt','r') as f:
    score_list = f.readline().rstrip().split(",")

# Convert to list of int
score_list = [int(v) for v in score_list]

print score_list

answered Jan 23, 2016 at 16:50

desa

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2 Comments

Gabriel A. Over a year ago

Definitely helpful. Can I just ask: What does the '.rstrip()' and '.split() ' functions do? Thanks

desa Over a year ago

Sure, rstrip function removes line endings and split(",") separates a string on ","

Rein · Accepted Answer · 2016-01-23 17:03:55Z

2

Just use split on comma on each line and add the returned list to your score_list, like below:

opener = open('scores.txt','r')
score_list = []

for line in opener:
    score_list.extend(map(int,line.rstrip().split(',')))

print( score_list )

edited Jan 23, 2016 at 17:03

answered Jan 23, 2016 at 16:51

Rein

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2 Comments

Martijn Pieters Over a year ago

You should really use score_list.extend() or use score_list += to avoid creating new lists all the time.

Rein Over a year ago

@MartijnPieters Thanks. Updated my answer to use extend

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