The following modules on the Python package index make standard library functionality from later versions of Python available in earlier versions (not all of them are technically backports - some existed on PyPI before being adopted wholesale into the standard library).
- faulthandler (Python 3.3+ faulhandler for 2.x and earlier versions of 3.x)
- configparser (Python 3.2+ configparser for 2.x)
- subprocess32 (provides equivalent functionality to the standard library's subprocess module as of Python 3.2)
- unittest2 (provides equivalent functionality to the standard library's unittest module as of Python 2.7/3.2)
contextlib2 (provides ExitStack, in the standard library's contextlib module as of Python 3.3)
- funcsigs (in the standard library's inspect module as of Python 3.3)
- futures (in the standard library as concurrent.futures as of Python 3.2)
- mock (in the standard library as unittest.mock as of Python 3.3)
- cdecimal (default implementation for the standard library's decimal module as of Python 3.3)
- enum34 (in the standard library as enum as of Python 3.3)
- singledispatch (in the standard library's functools module as of Python 3.4)
logutils (logging functionality added in 3.2+, such as QueueHandler/QueueListener)
The following modules on PyPI inspired later standard library additions, but have different APIs:
- flufl.enum (initial inspiration for what became the standard library's )
- ipaddr (initial inspiration for the standard library's ipaddress module as of Python 3.3)