Converting ConfigParser values to python data types

For those that may be looking for another easier answer, instead of having to convert the data types yourself, you can use the localconfig module that does the conversion for you. The conversion is done by guessing the data type based on the value (I.e. 123 is an int, 123.4 is a float, true is a bool, and so on).

Here is an example following the OP's:

>>> from localconfig import config
>>> config.read('[one]\nkey = 42\nkey2 = None')
>>> config.one.key, type(config.one.key)
(42, <type 'int'>)
>>> config.one.key2, type(config.one.key2)
(None, <type 'NoneType'>)
>>> config.get('one', 'key'), config.get('one', 'key2')
(42, None)

It is a wrapper on top of ConfigParser, so it is fully compatible.

Check it out at https://pypi.python.org/pypi/localconfig

If you are using Python 2.6 or above you can use ast.literal_eval:

ast.literal_eval(node_or_string)
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.

This will work like eval when the string is safe:

>>> literal_eval("{'key': 10}")
{'key': 10}

But it will fail if anything besides the types listed in the documentation appear:

>>> literal_eval("import os; os.system('rm -rf somepath')")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.6/ast.py", line 49, in literal_eval
    node_or_string = parse(node_or_string, mode='eval')
  File "/usr/lib64/python2.6/ast.py", line 37, in parse
    return compile(expr, filename, mode, PyCF_ONLY_AST)
  File "<unknown>", line 1
    import os; os.system('rm -rf somepath')
         ^
SyntaxError: invalid syntax