What does the 'b' character do in front of a string literal?

Question

Apparently, the following is the valid syntax:

my_string = b\'The string\'

I would like to know:

1. What does this b

Answer 1

Here's an example where the absence of b would throw a TypeError exception in Python 3.x

>>> f=open("new", "wb")
>>> f.write("Hello Python!")
Traceback (most recent call last):
  File "", line 1, in 
TypeError: 'str' does not support the buffer interface

Adding a b prefix would fix the problem.