help(f.write)
write(...)
write(str) -> None. Write string str to file.
Note that due to buffering, flush() or close() may be needed before
the file on disk reflects the data written.
養成help一下的好習慣
The optional size argument, if given, is an approximate bound on the? ? total number of bytes in the lines returned.不給這個參數 就是 讀出全部，給任意參數 就是讀出系統緩存大小相近個字節
