Converting ConfigParser values to python data types

Question

ConfigParser requires all sections, keys and values to be strings; no surprise. It has methods to convert the values to datatypes with getfloat, getint, getboolean. If you don't know the datatype, you can wrap the get() with an eval() to get have the string evaluated such as:

>>> from ConfigParser import SafeConfigParser
>>> cp = SafeConfigParser()
>>> cp.add_section('one')
>>> cp.set('one', 'key', '42')
>>> print cp.get('one', 'key')
'42'
>>> print eval(cp.get('one', 'key'))
42
>>> cp.set('one', 'key', 'None')
>>> print eval(cp.get('one', 'key'))
None
>>>

Is there a better way? I assume there some grave security concerns with evaluating text from a file- which I acknowledge; I completely trust the file.

I thought I would use pickle for this, but I would really like to keep the config file human readable.

How would you do it?

Andrew Clark · Accepted Answer · 2011-06-02 00:12:24Z

17

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

answered Jun 2, 2011 at 0:12

Andrew Clark

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1 Comment

tMC Over a year ago

i used your answer to create this: codereview.stackexchange.com/questions/2775/…

Max Zheng · Accepted Answer · 2015-01-02 03:59:35Z

6

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

edited Jan 2, 2015 at 3:59

answered Jan 2, 2015 at 3:36

Max Zheng

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1 Comment

nathan.j.mcdougall Mar 18 at 5:25

Disclaimer: Answerer is the package author.

Erik Kalkoken · Accepted Answer · 2021-02-10 21:33:10Z

5

Here is an another solution. You can generate a getany() method that will automatically detect and return the correct data type for most types including str, int, float, bool and None.

Note that the notation in the config file needs to be Python for this to work. e.g. True for boolean true and None for null values.

from ast import literal_eval
import configparser

parser = configparser.ConfigParser(converters={"any": lambda x: literal_eval(x)})
value = parser.getany("section", "key")
# ...

answered Feb 10, 2021 at 21:33

Erik Kalkoken

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2 Comments

Nils Werner Over a year ago

This doesn't work for simple string values, does it? key=1.0 is fine, but key=test isn't...

Erik Kalkoken Over a year ago

yes. As mentioned it only works for values in Python notation.

Kaushik Ghose · Accepted Answer · 2013-07-10 20:42:53Z

1

If you are on 2.7+ then you can use the .getint .getfloat .getbool methods. You can learn more about them in the docs

So your application would use print cp.getint('one', 'key')

answered Jul 10, 2013 at 20:42

Kaushik Ghose

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Comments

Justin · Accepted Answer · 2014-02-10 02:35:04Z

0

Checkout ConfigIt for more pythonic configuration options

https://github.com/barberj/ConfigIt

answered Feb 10, 2014 at 2:35

Justin

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Ankit Jain · Accepted Answer · 2024-01-11 11:14:42Z

0

Adding on to Erik Kalkoken's answer. You can probably write a converter function which gives you more control over how you want to evaluate the value.

def converter(in_str: str):
    try:
        out = literal_eval(in_str)
    except Exception:
        out = in_str
    return out

parser = configparser.ConfigParser(converters={"any": lambda x: converter(x)})
value = parser.getany("section", "key")

answered Jan 11, 2024 at 11:14

Ankit Jain

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