My expectation was that any defaults I passed to ConfigParser when creating one would override values in the DEFAULT section of the config file. This is because I'd like the DEFAULT section to have the default values, but then I want to be able to override those with settings from environment variables.

However, this is not the way it works. The defaults in the file take precedence over the defaults passed to the constructor. I didn't see a mention of this in the docs, but I might've missed it.

Take this short program (`configparsertest.py`):

```
import configparser

cp = configparser.ConfigParser({'foo': 'dog'})
print(cp.defaults())
cp.read('app.ini')
print(cp.defaults())
```

and this config file (`app.ini`):

```
[DEFAULT]
foo = bar
```

I was expecting that I would see foo equal to dog twice, but what I get is:

```
$ python configparsertest.py
OrderedDict([('foo', 'dog')])
OrderedDict([('foo', 'bar')])
```

The reason that I want the programmatic default values to override the default values in the file is that I want the file to have low-precedence defaults that are used as a last resort, and I want to be able to override the defaults with the values from environment variables.

As a concrete example, imagine that I have a config file for the stdlib `logging` module that looks something like this:

```
[DEFAULT]
logging_logger_root_level = WARN
...
[logger_root]
level = %(logging_logger_root_level)s
handlers = console
```

The desired behavior is that normally the app would use the WARN level for logging, but I'd like to be able to do something like:

```
$ LOGGING_LOGGER_ROOT_LEVEL=DEBUG python my_app.py
```

to get DEBUG logging.

Maybe there is some other mechanism to accomplish this?