Chapter 5 - Loops - Section 5.2 - The while Loop - Check Point - MyProgrammingLab - Page 142: 5.2

While loop in line 7 is skipped when variable number is set to 0.

If guess variable is initialized to 0 in line 8 in Listing 5.3 then in the case random integer number generated in line 3 is equal to 0 the while loop condition guess != number is False and the user doesn't get the chance to guess the random number generated.