I've only got 3.7.1 Ubuntu bash on Windows (also amd64) immediately available, but I'm not seeing a hang, nor is there any obvious memory leak that might eventually lead to problems (memory regularly drops back to under 10 MB shared, 24 KB private working set). I modified your code to add a sys.stdout.flush() after the write so it would actually echo the dots as they were written instead of waiting for a few thousand of them to build up in the buffer, but otherwise it's the same code.

Are you sure you're actually hanging, and it's not just the output getting buffered?