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2.Reproducing_the_bug.md

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2. Reproducing the BUG

Now there are programs that sometime might execute and sometime they might throw an error. Now that puts us in a weird situation.

like bro why do it work sometime and not other time?

Follow the following example

from random import randint 
numbers = ["1", "2", "3", "4", "5", "6"] 
select_a_number = randint(a: 1, b: 6) 
print(numbers[select_a_number])

Run this code, and you'll notice that it works most of the time but ocasionally throws an error.

What is our job? To find the bug duh

  1. We have to find when does that error actually happen?
  2. Try reproducing the bug yourself. (sometimes to destroy the monster you must reproduce the monster)
  3. Try to notice when it happens, what conditions lead up to the bug/error.
  4. Change the code so that it always produces the error.

Look at the following line of code:

select_a_number = randint(a:1,b:6)

This randint function chooses a number between 1 and 6 including the 1 and the 6 (This is not like the range function where it did not include the last number in the range.) When a number is chosen it is inserted into the numbers list to select a number from the list and print it.

print(numbers[select_a_number])
  • now when we pick a number from our list we are ocasionally getting an error.
  • This can point to the randint function being used
  • We look at the amount of numbers in a list that is 6.
  • We look at the randint which picks the number with the range from 1 to 6(including the 6)

Reproducing the bug

We will try picking the numbers in the list manually, to select each individual number. Putting 1 in the list.

select_a_number = 1

the output will be

output = 2

We repeat this untill we find the bug but also keep your eyes open for any weird behaviour like when we placed 1 in the list it selected the number 2(which is the second item in the list)

  • Putting 2 in the list.
select_a_number = 2

the output will be

output = 3
  • Putting 3 in the list.
select_a_number = 3

the output will be

output = 4
  • Putting 4 in the list.
select_a_number = 4

the output will be

output = 5
  • Putting 5 in the list.
select_a_number = 5

the output will be

* Putting 6 in the list.
output = 6

select_a_number = 6

the output will be

output = ERROR!!!!!!!!!

We have finally reproduced the error, The problem here is that the list index starts from 0 hence we never saw 1 being printed and for 6 elements it would go from 0 to 5 but the randint function is going 1 to 6. which tells us there is one element that is never being selected and at one index i.e., 6 there is no element which is the reason for our bug.