ConfigParser and String interpolation with env variable

Question

it's a little bit I'm out of python syntax and I have a problem in reading a .ini file with interpolated values.

this is my ini file:

[DEFAULT]
home=$HOME
test_home=$home

[test]
test_1=$test_home/foo.csv
test_2=$test_home/bar.csv

Those lines

from ConfigParser import SafeConfigParser

parser = SafeConfigParser()
parser.read('config.ini')

print parser.get('test', 'test_1')

does output

$test_home/foo.csv

while I'm expecting

/Users/nkint/foo.csv

EDIT:

I supposed that the $ syntax was implicitly included in the so called string interpolation (referring to the manual):

On top of the core functionality, SafeConfigParser supports interpolation. This means values can contain format strings which refer to other values in the same section, or values in a special DEFAULT section.

But I'm wrong. How to handle this case?

Answer 1

First of all according to the documentation you should use %(test_home)s to interpolate test_home. Moreover the key are case insensitive and you can't use both HOME and home keys. Finally you can use SafeConfigParser(os.environ) to take in account of you environment.

from ConfigParser import SafeConfigParser import os   parser = SafeConfigParser(os.environ) parser.read('config.ini') 

Where config.ini is

[DEFAULT] test_home=%(HOME)s  [test] test_1=%(test_home)s/foo.csv test_2=%(test_home)s/bar.csv 

Answer 2

You can write custom interpolation in case of Python 3:

import configparser
import os


class EnvInterpolation(configparser.BasicInterpolation):
    """Interpolation which expands environment variables in values."""

    def before_get(self, parser, section, option, value, defaults):
        value = super().before_get(parser, section, option, value, defaults)
        return os.path.expandvars(value)


cfg = """
[section1]
key = value
my_path = $PATH
"""

config = configparser.ConfigParser(interpolation=EnvInterpolation())
config.read_string(cfg)
print(config['section1']['my_path'])

Answer 3

If you want to expand some environment variables, you can do so using os.path.expandvars before parsing a StringIO stream:

import ConfigParser
import os
import StringIO

with open('config.ini', 'r') as cfg_file:
    cfg_txt = os.path.expandvars(cfg_file.read())

config = ConfigParser.ConfigParser()
config.readfp(StringIO.StringIO(cfg_txt))