Python programming changing a specific value in file

Question

I have a problem with concerning my code:

with open('Premier_League.txt', 'r+') as f:
    data = [int(line.strip()) for line in f.readlines()] # [1, 2, 3]
    f.seek(0)

    i = int(input("Add your result! \n"))

    data[i] += 1  # e.g. if i = 1, data now [1, 3, 3]

    for line in data:
        f.write(str(line) + "\n")

    f.truncate()
    print(data)

The code works that the file "Premier_League.txt" that contains for example:

1
2
3

where i=1 gets converted to and saved to already existing file (the previous info gets deleted)

1
3
3

My problem is that I want to chose a specific value in a matris (not only a vertical line) for example:

0 0 0 0
0 0 0 0
0 0 0 0

where i would like to change it to for example:

0 1 0 0
0 0 0 0
0 0 0 0

When I run this trough my program this appears:

ValueError: invalid literal for int() with base 10: '1 1 1 1'

So my question is: how do I change a specific value in a file that contains more than a vertical line of values?

Question: why 0 1 0 0 and not say 0 0 1 0 or any other combination? — Ma0
– Ma0, Commented Jul 19, 2017 at 11:50
No you should be able to change it to both, its just going in and changing a specific value in the file , therefore it can be both 0 1 0 0 or 0 0 1 0 or why not 0 1 1 0 — Argentum
– Argentum, Commented Jul 19, 2017 at 11:52
This is the very definition of an XY problem. You are approaching the whole thing wrong. — Ma0
– Ma0, Commented Jul 19, 2017 at 11:57
Maybe consider providing column names and handle it like a csv instead? It might make things much easier to handle as well when wanting to change data. — idjaw
– idjaw, Commented Jul 19, 2017 at 11:59
Also you prompt the user to add his result but instead you simply use the input to jump to the corresponding line and increment the content by 1.. — Ma0
– Ma0, Commented Jul 19, 2017 at 12:02

Tom Wyllie · Accepted Answer · 2017-07-19 12:00:17Z

3

The problem is you are not handling the increased number of dimensions properly. Try something like this;

with open('Premier_League.txt', 'r+') as f:
    # Note this is now a 2D matrix (nested list)
    data = [[int(value) for value in line.strip().split()] for line in f ]
    f.seek(0)

    # We must specify both a column and row
    i = int(input("Add your result to column! \n"))
    j = int(input("Add your result to row! \n"))

    data[i][j] += 1 # Assign to the index of the column and row

    # Parse out the data and write back to file
    for line in data:
        f.write(' '.join(map(str, line)) + "\n")

    f.truncate()
    print(data)

You could also use a generator expression to write to the file, for example;

# Parse out the data and write back to file
f.write('\n'.join((' '.join(map(str, line)) for line in data)))

instead of;

# Parse out the data and write back to file
for line in data:
    f.write(' '.join(map(str, line)) + "\n")

answered Jul 19, 2017 at 12:00

Tom Wyllie

2,08215 silver badges16 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Argentum Over a year ago

And just a question, the two examples; do they basically act the same?

Argentum Over a year ago

Is it just that the first one is simpler written? ^^

Tom Wyllie Over a year ago

The first one is one line less code, but they basically do the same thing.

Tom Wyllie Over a year ago

If you want to get technical I suppose the second one uses more write operations but less memory, I prefer it just because I think it's more elegant, but it's harder to understand to I included both.

dheiberg · Accepted Answer · 2017-07-19 12:09:25Z

1

First up, you are trying to parse the string '0 0 0 0' as an int, that's the error you are getting. To fix this, do:

data = [[int(ch) for ch in line.strip().split()] for line in f.readlines()]

This will create a 2D array, where the first index corresponds to the row, and the second index corresponds to the column. Then, you would probably want the user to give you two values, instead of a singular i since you are trying to edit in a 2D array.

Edit:
So your following code will look like this:

i = int(input("Add your result row: \n"))
j = int(input("Add your result column: \n"))

data[i][j] += 1  
# For data = [[1,2,1], [2,3,2]], and user enters i = 1
# and j = 0, the new data will be [[1,2,1], [3,3,2]]

edited Jul 19, 2017 at 12:09

answered Jul 19, 2017 at 11:56

dheiberg

1,93415 silver badges18 bronze badges

2 Comments

Argentum Over a year ago

I am not compleatly sure I understand you. Do you mean I should change my data = [int(line.strip()) for line in f.readlines()] # [1, 2, 3] into data = [[int(ch) for ch in line.strip().split(' ')] for line in f.readlines()], but the program tells me that: TypeError: 'int' object is not iterable

dheiberg Over a year ago

Sorry there was a slight bug, it should be split() not split(' '). But the user Tom Wyllie has already addressed it

Collectives™ on Stack Overflow

Python programming changing a specific value in file

2 Answers 2

4 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related