@jacobian 

It seems the ```.headers``` property is not available in HTTPResponse when using python2. Try this:

```python
import librato
import os
api = librato.connect(os.environ['LIBRATO_USER'], os.environ['LIBRATO_TOKEN'])
metrics = api.list_metrics()
```

```
$ python3 play.py
$ python2 play.py
Traceback (most recent call last):
  File "play.py", line 4, in <module>
    metrics = api.list_metrics()
  File "/Users/drio/dev/librato/python-librato/librato/__init__.py", line 175, in list_metrics
    resp = self._mexe("metrics", query_props=query_props)
  File "/Users/drio/dev/librato/python-librato/librato/__init__.py", line 150, in _mexe
    resp_data, success, backoff = self._process_response(resp, backoff)
  File "/Users/drio/dev/librato/python-librato/librato/__init__.py", line 127, in _process_response
    resp_data = json.loads(body.decode(resp.headers.get_content_charset('utf-8')))
AttributeError: HTTPResponse instance has no attribute 'headers'
```