Python file read/write mode

' B ' and binary binary
' R '--and read read
' W ' and write writing
' A '-and append append

So: ' RB ' is reading the file in binary form

Note:
The difference between ' W ' and ' a ':
' W ' mode, this file will be created if the file does not exist; If the file exists, overwrite it
' A ' mode, open a file for appending, that is, the file pointer will point to the end of the file; Of course, this file will be created if the file does not exist.

As for ' + ', this good understanding.
' r+ ' and ' WR '
' w+ ' and ' WR '

The original is read, more than a ' + ', and can read, and can write;
Similarly, the original is write, more than a ' + ', and can write, and can read.

Python file read/write mode