How can I read a string in a file formated as a list into a list in Python?

Question

I have a string formatted as a list of lists in a file. How can I get this into a variable in Python as a list?

E.g. data-string.txt

with open('data-string.txt') as f:
    str = f.read()

and

str = "[[1, 2, 3], [2, 3, 4], [3, 4, 5]]"

are equivalent. How can I get this into a real Python list? I have looked into splitting using multiple delimiters, but if that's the right way I haven't been able to set it up correctly.

score 3 · Accepted Answer · answered Mar 01 '19 at 22:40

3

You may use ast.literal_eval() to do your bidding:

import ast
s = ast.literal_eval("[1,2,3]")
s == [1,2,3]

answered Mar 01 '19 at 22:40

Bharel

23,672
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Fantastic. Never heard of abstract syntax trees before. Thank you! – M. Thompson Mar 01 '19 at 22:44

score 1 · Answer 2 · answered Mar 01 '19 at 22:43

1

You can use json for some cases, but @Bharel answer is better at all

import json

with open('data-string.txt') as f:
    lst = json.load(f)
    print(lst)  # [[1, 2, 3], [2, 3, 4], [3, 4, 5]]

answered Mar 01 '19 at 22:43

sanyassh

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This actually solves my purpose as well. Thank you. – M. Thompson Mar 01 '19 at 23:03

score -1 · Answer 3 · answered Mar 01 '19 at 22:47

How about this:

// convert original string to type list
str1 = list("[[1, 2, 3], [2, 3, 4], [3, 4, 5]]")

// create a new string using the following, which converts same to a 3 x 3 list
str2 = ''.join(str(e) for e in str1)

// prints out as [[1, 2, 3], [2, 3, 4], [3, 4, 5]]

// https://stackoverflow.com/questions/5618878/how-to-convert-list-to-string

How can I read a string in a file formated as a list into a list in Python?

3 Answers3