When I run sys.stdin.readline() interactivelly (on Windows and Python 3.3.2) and hit Ctrl-C, sometimes it returns an empty string just before KeyboardInterrupt is raised. Sometimes it isn't even raised and instead after hitting Return some weird SyntaxtError: unknown decode error (on line 0) occurs. Seems like propagation of KeyboardInterrupt is somehow out of sync. sys.stdin.read(n) has the same issue. May be related to recently fixed http://bugs.python.org/issue17619 where was similar situation with input().