How can I build a python datastructure by reading it from a file

Question

I would like to build a list or a list of list by reading it from a text file.

For example, I have a file 'mylist.txt' saying

mylist = [
1,
2,
3,
4]

myotherlist = [
 [1, 3, 4, 5],
 [3, 5, 3, 6]
]

I would like to read that text file and then use that in my python script.

Is that possible? I just use the above example in python syntax. My goal is to avoid writing parsing logic myself. And XML seems to be too complicated for my purpose.

Thank you.

Answer 1

If I had the following data file (data.txt):-

[1,2,3,4]

Then this code would read it into a list.

from ast import literal_eval

with open('data.txt') as fsock:
   mylist = literal_eval( fsock.read() )

This will also work for other datatypes e.g. dictionaries. See literal_eval docs for more details.

Answer 2

If it's a list of lists, then you should just define it "straight up" in your mylists.txt file.

e.g.

MYLISTS = [
    [1, 2, 3],
    [2, 3, 4],
    ...
]

And rename mylists.txt to mylists.py.

Then, with another Python script in the same directory, you can just do

import mylists
for sublist in mylists.MYLIST:
    for elem in sublist:
        ....

This requires no parsing code on your part, and the Python "data" file is very easy to hand-edit, too.