Question

Say I have a string representing some nested lists and I want to convert it into the real thing. I could do this, I think:

exec "myList = ['foo', ['cat', ['ant', 'bee'], 'dog'], 'bar', 'baz']"

But in an environment where users might be supplying the string to execute this could/would be a bad idea. Does anybody have any ideas for a tidy parser that would accomplish the same thing?

Answer 1

>>> import ast
>>> mylist = ast.literal_eval("['foo', ['cat', ['ant', 'bee'], 'dog'], 'bar', 'baz']")
>>> mylist
['foo', ['cat', ['ant', 'bee'], 'dog'], 'bar', 'baz']

ast.literal_eval:

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

This can be used for safely evaluating
strings containing Python expressions
from untrusted sources without the
need to parse the values oneself.