Python: index out of range but I can't see why - indexing

Question

I'm trying to code a program that opens a file, creates a list that contains each line of this file, and removes some words from this list. I have an Index Out of Range error.
#! /usr/bin/python3
# open the file
f = open("test.txt", "r")
# a list that contains each line of my file (without \n)
lines = f.read().splitlines()
# close the file
f.close()
# some words I want to delete from the file
data = ["fire", "water"]
# for each line of the file...
for i in range(len(lines)):
# if this line is in [data]
if lines[i] in data:
# delete this line from [data]
print(lines[i])
del lines[i]
This is my text file:
sun
moon
*
fire
water
*
metal
This is my output:
fire
Traceback (most recent call last):
File "debug.py", line 16, in <module>
if lines[i] in data:
IndexError: list index out of range

Answer 1

I'll address the out of index error first.
What's happening, in your first post, is that it takes the length of the list
which is 7, so len(lines) = 7 which will result in range(7) = (0,7) which will do this:
lines[0] = sun
lines[1] = moon
lines[2] = *
lines[3] = fire
lines[4] = water
lines[5] = *
lines[6] = metal
=>
lines[0] = sun
lines[1] = moon
lines[2] = *
deleted lines[3] = fire
lines[3] = water
lines[4] = *
lines[5] = metal
If you now delete lines[3] it will still try to iterate over lines[6] although it won't exist anymore.
It will also continue to iterate over the next index lines[4] so water will never be checked, it is absorbed.
I hope this helps and I suggest you do this instead:
# open the file
f = open("test.txt", "r")
# a list that contains each line of my file (without \n)
lines = f.read().splitlines()
# close the file
f.close()
# some words I want to delete from the file
data = ["fire", "water"]
for i in data:
if i in lines:
lines.remove(i)
print(lines)
Output:
['sun', 'moon', '', '', 'metal']