How can I convert string to dict or list?

Question

I have strings such as:

'[1, 2, 3]'

and

"{'a': 1, 'b': 2}"

How do I convert them to list/dict?

Someone mentions that ast.literal_eval or eval can parse a string that converts to list/dict.

What's the difference between ast.literal_eval and eval?

Answer 1

ast.literal_eval parses 'abstract syntax trees.' You nearly have json there, for which you could use json.loads, but you need double quotes, not single quotes, for dictionary keys to be valid.

import ast

result = ast.literal_eval("{'a': 1, 'b': 2}")
assert type(result) is dict

result = ast.literal_eval("[1, 2, 3]")
assert type(result) is list

As a plus, this has none of the risk of eval, because it doesn't get into the business of evaluating functions. eval("subprocess.call(['sudo', 'rm', '-rf', '/'])") could remove your root directory, but ast.literal_eval("subprocess.call(['sudo', 'rm', '-rf', '/'])") fails predictably, with your file system intact.

Answer 2

Use the eval function:

l = eval('[1, 2, 3]')

d = eval("{'a':1, 'b': 2}")

Just make sure you know where these strings came from and that you aren't allowing user input to be evaluated and do something malicious.

Answer 3

python script to convert this string to dict : -

import json

inp_string = '{"1":"one", "2":"two"}'
out = json.loads(inp_string)
print out["1"]

O/P is like :

"one"

Answer 4

You can eval() but only with safe data. Otherwise, if you parse unsafe data, take a look into safer ast.literal_eval().

JSON parser is also a possibility, most of python dicts and lists have the same syntax.

Answer 5

You can convert string to list/dict by ast.literal_eval() or eval() function. ast.literal_eval() only considers a small subset of Python's syntax to be valid:

The string or node provided may only consist of the following Python literal structures: strings, numbers, tuples, lists, dicts, booleans, and None.

Passing __import__('os').system('rm -rf /') into ast.literal_eval() will raise an error, but eval() will happily wipe your drive.

Since it looks like you're only letting the user input a plain dictionary, use ast.literal_eval(). It safely does what you want and nothing more.