Call sem.release(5) would have the same effect as:

with lock:
    for i in range(5):
         sem.release()

The use case is when a single semaphore is holding up multiple threads and needs to release them all.  According to "The Little Book of Semaphores <http://greenteapress.com/semaphores/>", this is a common design pattern.

Basic patch attached.  If the proposal meets with acceptance, will add tests and a doc update.

Your patch uses tabs for indentation. Otherwise, looks good on the principle.

Seems good to proceed as there are no dissenters.

Updated patch (with tests and docs).

Never know whether to comment on issue itself, but just in case:

There are issues with the patch when n < 0 is passed, as n is not sanity checked, which would break the Semaphore invariant (value must be >= 0). n == 0 is also a weird value, but harmless if passed; release(0) would acquire and release the lock but otherwise act as a noop.

New changeset 35f6301d68bdb0517be284421782d64407dfe72c by Raymond Hettinger in branch 'master':
bpo-10978: Semaphores can release multiple threads at a time (GH-15588)
https://github.com/python/cpython/commit/35f6301d68bdb0517be284421782d64407dfe72c