sloria/webargs — pull request #15 by jmcarp (2014-10-12 03:42:09+00:00)
Title: Add optional source parameter to Arg.

For use when values are keyed on variable-unsafe names, or when the developer just wants to rename keys:
```python
args = {
'content_length': Arg(source='Content-Length'),
'query': Arg(source='q'),
}
```