I built random-2.patch on my windows xp box (updating the project and fixing some compile errors in random.c required), and initialising crypto has a noticeable impact on startup time. The numbers vary a fair bit naturally, two representative runs are as follows: changeset 52796:1ea8b7233fd7 on default branch: >timeit %PY3K% -c "import sys;print(sys.version)" 3.3.0a0 (default, Jan 7 2012, 00:12:45) [MSC v.1500 32 bit (Intel)] Version Number: Windows NT 5.1 (Build 2600) Exit Time: 0:16 am, Saturday, January 7 2012 Elapsed Time: 0:00:00.218 Process Time: 0:00:00.187 System Calls: 4193 Context Switches: 445 Page Faults: 1886 Bytes Read: 642542 Bytes Written: 272 Bytes Other: 31896 with random-2.patch and fixes applied: >timeit %PY3K% -c "import sys;print(sys.version)" 3.3.0a0 (default, Jan 7 2012, 00:58:32) [MSC v.1500 32 bit (Intel)] Version Number: Windows NT 5.1 (Build 2600) Exit Time: 0:59 am, Saturday, January 7 2012 Elapsed Time: 0:00:00.296 Process Time: 0:00:00.234 System Calls: 4712 Context Switches: 642 Page Faults: 2049 Bytes Read: 1059381 Bytes Written: 272 Bytes Other: 34544 This is with hot caches, cold will likely be worse, but a smaller percentage change. On a faster box, or with an SSD, or win 7, the delta will likely be smaller too. A 50-100ms slow down is consistent with the difference on Python 2.7 between calling `os.urandom(1)` or not. However, the baseline is faster with Python 2, frequently dipping under 100ms, so there this change could double the runtime of trivial scripts.