List arithmetic operation in python

Question

one problem statement on python list arithmetic that is I have one list say,

my_set = [24565,24621,32,598,899]

I want to take difference between first two elements and if difference is in range of -127 to 127 then add +128 to next index position and so on. First element of the list stays as-is

Like this the output

[24565, 56, +128, 24589, +128, −566, +128, -301].

this is what I tried to do

def inRange(val):
 return val in range(-127,127)
my_set = [24565,24621,32,598,899]
for i in range(len(my_set)-1):
 res = my_set[i] - my_set[i+1]
 if inRange(res) == True:
 my_set.insert(i+1,res)
 my_set.insert(i+2,128)
print(my_set) 

Please tell me how to do that.?? THankyou!

• KBN: Not quite clear. And modifying the list while iterating over it is not a good idea. So if the difference between two consecutive numbers is in the range of -127 to 127 you would want to add that difference value. And for each check you want to add +128?
• shahaf: can you explain how you get to the following output?
• Shriniwas: @KeerthiBachu yes what you got is right ..this is exactly what I want..... Actually this problem statement was asked me in interview. and interviewer was so clear about problem statement.
• Shriniwas: @shahaf which exactly??? the code which tried or the output which I shown above??

Answer 1

But in the desired output that you have written, you are adding 128 in spite of what the difference is. And you are also adding the difference value to the list. I got confused there. Anyways, this does adding the difference and 128 to the list. Also, can you make use of a new list to update the output or should you update the same list? The first case, its easy; the second case, you can try the below code

def inRange(val): # a simple if is enough and faster range
 if val < 127 and val >= -127:
 return True
my_set = [24565,24621,32,598,899]
#as you wanted the first element as is, moved this piece of code out of the loop
my_set.insert(1, my_set[0]-my_set[1])
my_set.insert(2,128)
i = 3
while i < len(my_set) - 1:
 res = my_set[i] - my_set[i+1]
 #if inRange(res) == True: # you can add this loop if required and do the inserts accordingly
 my_set[i] = res
 my_set.insert(i+1, 128)
 i = i + 2 # if you are gonna add the if check and insert only then, you might want to change the i increment as per that
print(my_set) 

Hope this helps. And expecting some one else to give a better answer :)

• Shriniwas: @at KeerthiBachu Thank you for answering...I tested your code...you are too damnn close to output...I studied your code ..but I couldn't got the output too. Still ..thanks again ....lets see if anyone answer it with 100% accuracy..
• KBN: If you are clear with the output that you need, you can modify the above code accordingly. Is the desired output that you mentioned in the question is what you need?