How to insert a number+1, +2 next to the position of that number in the list?

I want to be able to insert numbers +1 , +2 based off the number in the list, directly next to that number it is based off of.

Example:

# existing list
list1 = [1,10,100]

#wanted output: 
[1,2,3, 10,11,12, 100,101,102]

#I spaced out the output list for ease of reading/understanding what it is I want to do.

I would also like to be able to add up to +7 and more, so if it is possible please help make it efficient in this way.

Answer

You can use a simple nested comprehension:

list1 = [1, 10, 100]
n = 3  # or 7 or whatever


list2 = [x for y in list1 for x in range(y, y+n)]
# [1, 2, 3, 10, 11, 12, 100, 101, 102]