[Reading file] in python core, Why "for loop" not work in this practice?

Question

Hi, For the practice I use the code to show result pull up in each day

for the code It show result are correct :

file = open("/usercode/files/pull_ups.txt")
n = int(input())
line = file.readlines()
print(line[n])
file.close()

But when i used for loop it not work:

file = open("/usercode/files/pull_ups.txt")
n = int(input())
for line in file:
print(line[n])
file.close()

What different between readline and for loop when I read each line?

Answer 1

Oh I see ...
Well, you see, the readlines() returns a `list`, a container that supports item referencing by index. So your first snippet looks like a candidate because it refers an item from the list by a given index <n>.

Your second snippet though, you are not referencing n-th row in the file. Why is that so you ask me? because the `for line in file` reads in one line at a time, on each loop round. So the <line> here is a string representing a distinct line in the file, rather than the entire file content splitted into a `list`as readlines() presented earlier.

Now let's assume somewhere in the loop that <line> contains

"Day 5, 9 pullups\n"

And we go like

print( line[ n ] )

We expected to see the n-th row, but actually here we are referencing the n-th + 1 character from string <line>. In case <n> was 3, then we see the 4-th character of the string <line> (remember index begins with 0).

A possible issue here is when <n> was greater than length of <line> -1, we will get index out of bound error.

Answer 2

I forgot the task requirement, can you briefly describe it for me?

Answer 3

"for line in file:"
"file" is an object and not a string or list. You have to write "file.readlines()".
Although, I think you forget to write it in your question and maybe your question is actually about the blank lines between the outputs. In this case:
Each print() goes to the next line by default. And in each line, there is a "\n" character. So there is one blank line between the output lines. Which leads to failure in the tests.

[edit:] Thada Sukprasong
i didn't read the problem statement. if it wants just one line, then ignore the second part of my answer.

Answer 4

Tom has done pull ups every day and recorded his results. He recorded each day's results in a new line, so that each line represents each day he has done pull ups.
Create a program that takes n number as input and outputs the n-th days result (starting from 0).

Sample Input
4

Sample Output
Day 4, 9 pull ups

Answer 5

This practice say " recorded each day's results in a new line". So i think the data in the file are the

day 1
day 2
.
.
.

I think if it have the separate in new line for newday why i dont use for loop