range.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

l = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100]

pre = 1 
post = 1 
diff = 2

index = -1
for i in range(1, len(l)):
    d = l[i] - l[i-1]
    if d >= diff:
        index = i
        break

print(index)

target_l = []
for i in range(len(l)):
    if l[i] <= l[index-1] and l[index-1] - l[i] <= pre or l[i] >= l[index] and l[i]-l[index] <= post:
        target_l.append(l[i])

print(target_l)