python: create variable from loop that reads text file and extracts single column

Question

I'm new to python and was hoping for some assistance please.

I have a small script that reads a text file and prints only the fist column using a for loop:

list = open("/etc/jbstorelist")
for column in list:
    print(column.split()[0])

But I would like to take all the lines printed in the for loop and create one single variable for it.

In other words, the text file /etc/jbstorelist has 3 columns and basically I want a list with only the first column, in the form of a single variable.

Any guidance would be appreciated. Thank you.

declare a list before entering the loop: lst = [] and then replace print(column.split()[0]) with: lst.append(column.split()[0]) — Nir Alfasi
– Nir Alfasi, Commented Apr 7, 2017 at 15:32
Thanks alfasin. I do not quite understand this, so I did your request literarly as you have it. And am getting 1st = [] ^ SyntaxError: invalid syntax I must be misunderstanding how to implement the first part of your suggestion: 1st = [] Can you please demonstrate it writing the script over? — Keif
– Keif, Commented Apr 7, 2017 at 15:42
I got it. Thank you. Do you know any way of printing the list without the lines being separated by apostrophes and commas? — Keif
– Keif, Commented Apr 7, 2017 at 15:49

John · Accepted Answer · 2017-04-07 15:45:49Z

2

Since you're new to Python you may want to come back and refernce this answer later.

#Don't override python builtins. (i.e. Don't use `list` as a variable name)
list_ = []

#Use the with statement when opening a file, this will automatically close if
#for you when you exit the block
with open("/etc/jbstorelist") as filestream:
    #when you loop over a list you're not looping over the columns you're
    #looping over the rows or lines
    for line in filestream:
        #there is a side effect here you may not be aware of. calling `.split()`
        #with no arguments will split on any amount of whitespace if you only
        #want to split on a single white space character you can pass `.split()`
        #a <space> character like so `.split(' ')`
        list_.append(line.split()[0])

answered Apr 7, 2017 at 15:45

John

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1 Comment

Keif Over a year ago

Thanks for the info. I haven't checked this page in a while but the logic is clear to me now.

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