Migrating to 2.x

Compared with the 1.0 release, there were relatively few backwards incompatible changes, but there are still a few issues to be aware of with this major release.

For more details on the changes in this release including new APIs, links to the relevant GitHub issues and some of the bug fixes, read Cory's blog on the subject.

API Changes

There were a couple changes to how Requests handles exceptions. RequestException is now a subclass of IOError rather than RuntimeError as that more accurately categorizes the type of error. In addition, an invalid URL escape sequence now raises a subclass of RequestException rather than a ValueError.
```
requests.get('http://%zz/')   # raises requests.exceptions.InvalidURL
```
Lastly, httplib.IncompleteRead exceptions caused by incorrect chunked encoding will now raise a Requests ChunkedEncodingError instead.

The proxy API has changed slightly. The scheme for a proxy URL is now required.

proxies = {
"http": "10.10.1.10:3128",    # use http://10.10.1.10:3128 instead
}

# In requests 1.x, this was legal, in requests 2.x,
#  this raises requests.exceptions.MissingSchema
requests.get("http://example.org", proxies=proxies)

Behavioural Changes

Keys in the headers dictionary are now native strings on all Python versions, i.e. bytestrings on Python 2 and unicode on Python 3. If the keys are not native strings (unicode on Python 2 or bytestrings on Python 3) they will be converted to the native string type assuming UTF-8 encoding.
Values in the headers dictionary should always be strings. This has been the project's position since before 1.0 but a recent change (since version 2.11.0) enforces this more strictly. It's advised to avoid passing header values as unicode when possible.