存储文本文件中的列表

Question

I have a textfile that contains a list on the first line. How can I read the file and store the first line in a list? I want to store the first line as a complete list not as a string.

Example of the textfile:

[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]

Answer 1

It looks like your data is valid json:

>>> import json
>>> json.loads('[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]')
[[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]

To load it from a file:

with open('my_file.txt') as f:
    my_list = json.load(f)

Similarly, yaml.load and ast.literal_eval could also handle that data.

Answer 2

You can use the ast module

import ast

s = '[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]'
s = ast.literal_eval(s)
print s, type(s)

>>> [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]] <type 'list'>

Answer 3

You can use ast.literal_eval() like below:

>>> import ast
>>>
>>> ast.literal_eval('[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]')
[[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]

This is why you should use ast.literal_eval() to evaluate your string:

ast.literal_eval(node_or_string)

Safely evaluate an expression node or a string containing a Python literal or container display. The string or node provided may only consist of the following Python literal structures: strings, bytes, numbers, tuples, lists, dicts, sets, booleans, and None.