Advent of Code 2017 - Day 5 - Python 3

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

"""Day 5 -- Advent of Code 2017"""

# Open and parse input to form our list of jump instructions.
with open('Day5input.txt', 'r') as f:
    instructions = list(map(int, [s.strip() for s in f.readlines()]))

# test = [0, 3, 0, 1, -3]
# instructions = test
cnt = 0
cur_index = 0
while True:
    # print(test)
    try:
        jump_val = instructions[cur_index]
        next_index = cur_index + jump_val
        # instructions[cur_index] += 1  # PART ONE
        instructions[cur_index] += (-1 if jump_val >= 3 else 1)  # PART TWO
        cur_index = next_index
    except IndexError:
        break
    cnt += 1

print(cnt)