彙總：
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