循环语句
http://www.runoob.com/python/python-loops.html http://www.runoob.com/python/python-while-loop.html http://www.runoob.com/python/python-for-loop.html http://www.runoob.com/python/python-nested-loops.html http://www.runoob.com/python/python-break-statement.html http://www.runoob.com/python/python-continue-statement.html http://www.runoob.com/python/python-pass-statement.html