Game Development Reference
In-Depth Information
7 - Using the Debugger
Figure 7-4: The Debug Control window.
The
number1
variable has the value
9
and the
number2
variable has the value
10
.
When you click Step, the program will display the string in the
print()
call with these
values. (Of course, we use the
str()
function so that we can concatenate the string
version of these integers.)
Clicking on Step on line 5 will cause the debugger to wait until the player enters a
response. Go ahead and type in the correct answer (in my case, 19) into the interactive shell
window. The debugger will resume and move down to line 6.
Line 6 is an
if
statement. The condition is that the value in
answer
must match the
sum of
number1
and
number2
. If the condition is
True
, then the debugger will move to
line 7. If the condition is
False
, the debugger will move to line 9. Click Step one more
time to find out where it goes.
The debugger is now on line 9! What happened? The condition in the
if
statement must
have been
False
. Take a look at the values for
number1
,
number2
, and
answer
.
Notice that
number1
and
number2
are integers, so their sum would have also been an
integer. But
answer
is a string. That means that the
answer == number1 +
number2
condition would have evaluated to
'19' == 19
. A string value and an integer
value will always not equal each other, so the condition would have evaluated to
False
.
That is the bug in the program. The bug is that we use
answer
when we should be using
int(answer)
. Go ahead and change line 6 to use
int(answer) == number1 +
number2
instead of
answer == number1 + number2
, and run the program again.
What is 2 + 3?
5
Correct!
This time, the program worked correctly. Run it one more time and enter a wrong answer
on purpose to make sure the program doesn't tell us we gave the correct answer. We have
now debugged this program. Remember, the computer will run your programs exactly as
you type them, even if what you type is not what you intend.
