Get lists by reading file in Python

Question

There is a matter that I can't resolve in Python.

I'm trying to get lists by reading file (like .xml or .txt).

I've put my lists in a big list in my file like it :

[[48,49,39,7,13,1,11],[46,27,19,15,24,8,4],[35,5,41,10,31,5,9],[12,9,22,2,36,9,2],[50,47,25,6,42,3,1]]

Now I'm looking for code to get this big list like a list, not like a string. In deed, I've already try some parts of code with open(), write() and read() functions. But Python returned me :

'[[48,49,39,7,13,1,11],[46,27,19,15,24,8,4],[35,5,41,10,31,5,9],[12,9,22,2,36,9,2],[50,47,25,6,42,3,1]]'

And it isn't a list, just a string. So I can't use list's functions to modify it.

Thanks for those who will answer to my problem

Community · Accepted Answer · 2017-05-23 12:28:43Z

7

well, a simple way is to parse it as a json string:

>>> import json
>>> l_str = '[[48,49,39,7,13,1,11],[46,27,19,15,24,8,4],[35,5,41,10,31,5,9],[12,9,22,2,36,9,2],[50,47,25,6,42,3,1]]'
>>> l = json.loads(l_str)
>>> print l
[[48, 49, 39, 7, 13, 1, 11], [46, 27, 19, 15, 24, 8, 4], [35, 5, 41, 10, 31, 5, 9], [12, 9, 22, 2, 36, 9, 2], [50, 47, 25, 6, 42, 3, 1]]

if you want to load a file that only contains that string, you can simply do it using the following:

>>> import json
>>> with open('myfile') as f:
>>>     l = json.load(f)
>>>     print l
[[48, 49, 39, 7, 13, 1, 11], [46, 27, 19, 15, 24, 8, 4], [35, 5, 41, 10, 31, 5, 9], [12, 9, 22, 2, 36, 9, 2], [50, 47, 25, 6, 42, 3, 1]]

But if what you want is to serialize python objects, then you should instead use pickle that's more powerful at that task…

Of course, there are other ways that others may give you to parse your string through an eval()-like function, but I strongly advice you against that, as this is dangerous and leads to insecure code. Edit: after reading @kamikai answer, I'm discovering about ast.literal_eval() which looks like a decent option as well, though json.loads() is more efficient.

edited May 23, 2017 at 12:28

CommunityBot

11 silver badge

answered Feb 22, 2014 at 11:34

zmo

24.9k4 gold badges58 silver badges91 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

zx81 Over a year ago

+1. Been enjoying cruising through your regex and Python answers. :)

lanzz · Accepted Answer · 2014-02-22 11:34:22Z

1

If your example is truly representative of your data (i.e., your text file contains only a list of lists of integers), you can parse it as JSON:

import json
data = read_the_contents_of_the_file()
decoded = json.loads(data)

Replace data = read_the_contents_of_the_file() with your existing code for reading the contents as string.

answered Feb 22, 2014 at 11:34

lanzz

43.4k12 gold badges93 silver badges99 bronze badges

Comments

Kamikai · Accepted Answer · 2014-02-22 11:40:16Z

1

As seen here, the inbuilt ast module is probably your best bet, assuming the text is still valid python.

import ast

ast.literal_eval("[[1,2,3], [4,5,6], [7,8,9]]") # Returns nested lists

answered Feb 22, 2014 at 11:40

Kamikai

1851 silver badge6 bronze badges

Comments

tmr232 · Accepted Answer · 2014-02-22 11:38:05Z

0

Use json to load and parse the file:

import json
with open(my_file_path, "rb") as f:
    my_list = json.load(my_file_path)

answered Feb 22, 2014 at 11:38

tmr232

1,21115 silver badges25 bronze badges

Collectives™ on Stack Overflow

Get lists by reading file in Python

4 Answers 4

1 Comment

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related