I get the following exception when running the release script:

[INFO] Step 6: Uploading Artifacts
Traceback (most recent call last):
File "./bin/release.py", line 367, in <module>
release()
File "./bin/release.py", line 332, in release
do_task(upload_artifacts, [base_dir % "as-modules", version], async_processes)
TypeError: not all arguments converted during string formatting

Seems like there's an incorrect string concatenation at line 332:

  do_task(upload_artifacts, [base_dir % "as-modules", version], async_processes)

Using string concatenation seems to solve the problem:

do_task(upload_artifacts, [base_dir + "/as-modules", version], async_processes)