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).

• selectors (Python 3.4+ selectors for 2.6, 2.7 and 3.3)

• 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 2.7 and 3.2+, such as dictConfig / QueueHandler / QueueListener)

• argparse (included in the standard library since Python 2.7/3.2)

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)