程序代码：

r              open text file for reading
w              truncate to zero length or create text file for writing
wx             create text file for writing
a              append; open or create text file for writing at end-of-file
rb             open binary file for reading
wb             truncate to zero length or create binary file for writing
wbx            create binary file for writing
ab             append; open or create binary file for writing at end-of-file
r+             open text file for update (reading and writing)
w+             truncate to zero length or create text file for update
w+x            create text file for update
a+             append; open or create text file for update, writing at end-of-file
r+b  or rb+    open binary file for update (reading and writing)
w+b  or wb+    truncate to zero length or create binary file for update
w+bx or wb+x   create binary file for update
a+b  or ab+    append; open or create binary file for update, writing at end-of-file