Convert String to List in Python Without Using Eval?

Question

I have a string, something like this: "[['Cheese', 72], ['Milk', 45], ['Bread', 22]]".

I want to convert this to a list. I know I can use eval(string) to get the list, but eval scares me because of its potential for catastrophe (and because I can get a non-list as valid output). Is there another saner/safer way to turn this string into a list? I know it's a list and anything that isn't a list is invalid data (and should be checked for and/or throw an error).

Answer 1

If you insist on doing it this way, you can use the ast.literal_eval function.

>>> import ast
>>> foo = "[['Cheese', 72], ['Milk', 45], ['Bread', 22]]"
>>> ast.literal_eval(foo)
[['Cheese', 72], ['Milk', 45], ['Bread', 22]]

I'm sure others will tell you that you're likely doing something wrong, or to use a library like JSON to transport arbitrary data structures like this one, and I wouldn't disagree.

Answer 2

Try to use the json module:

import json
s = "[['Cheese', 72], ['Milk', 45], ['Bread', 22]]"
s = s.replace("'", '"')
print json.loads(s)

Answer 3

You might consider using the json module to deserialize and making sure your strings are in json format.

See http://docs.python.org/2/library/json.html for details about using this module.

Answer 4

Here's one way: exec("list = "+foo) This should make a variable 'list' with the list in string converted to a real list. This also works for dictionaries, arrays, bools, etc in strings.