How to save contents of a list to a file?

Question

I have some question about my code:

def entry_book():
    book = ["autor", "ime", "godina", "ISNB", "zanr", "cena", "broj"]
    print ("Podaci za knjigu:")
    book[0] = input ("Autor: ")
    book[1] = input ("Naslov: ")
    book[2] = input ("Godina: ")
    book[3] = input ("ISNB: ")
    book[4] = input ("Zanr: ")
    book[5] = input ("Cena: ")
    book[6] = input ("Kolicina: ")
    record= "{}|{}|{}|{}|{}|{}|{}".format (book[0], book[1], book[2], book[3],
                                           book[4], book[5], book[6])

    print (book)
    print (record)
    f = open('books.txt','w')
    f.write (record)
    f.close()
    f = open("books.txt")
    x = f.read()
    f.close()
    print (x)
    record1 = record.split('|')
    print (record1)

    second_meni()

This is code to store information on books, which I want to access later (like at a library). However, every time I add/create a new book, the old one gets deleted. Can anyone help me rewrite the code so it can store the old data as well. Or please explain what is the correct way to do it?

`f = open('knjige.txt','w')`: it overwrites the file each time (truncates) — Jean-François Fabre, Jan 13 '17 at 15:35
Honestly, you really need to attend those free python course in codeacademy, etc to program this properly. — mootmoot, Jan 13 '17 at 15:42
Oh, and since you seem to be new here, @alex: upvote the answers that are helpful, and accept an answer as solution if that solved your problem. That's how StackOverflow keeps functioning... — Jochem Schulenklopper, Jan 13 '17 at 15:47
@JochemSchulenklopper i would but i don't have the 15rep. points for everyone to see that i upvoted it — Alex, Jan 13 '17 at 15:58

score 6 · Answer 1 · edited May 23 '17 at 12:16

6

You have to use

f = open('knjige.txt', 'a')

'w' recreates the file (so use it only for NEW files, or if you don't mind it will be overwritten, 'a' appends to a file.

See python open built-in function: difference between modes a, a+, w, w+, and r+?

Also some unrelated suggestions:

Use the add instead of indices, or even better: use a dictionary
Use English variable names/comments.
Use code to check if the file read/write is ok, what if the file cannot be written because of access restrictions or too less space on the disk?
Use different functions for the input, writing and printing, it makes testing/maintainability/extension much easier.

edited May 23 '17 at 12:16

Community

1
1

answered Jan 13 '17 at 15:35

Michel Keijzers

15,025
28
93
119

Thanks. It helped. But if i may ask one more question how do i create it so that every time i input a new book (list) it gets saved in a new row in the text file. – Alex Jan 13 '17 at 15:42
1

"how do i create it so that every time i input a new book (list) it gets saved in a new row in the text file": You should add a newline character to your output string, `\n`. – Jochem Schulenklopper Jan 13 '17 at 15:45
@Alex You need to put a newline at the end of the line of data. Eg, you can do what Ev's code does, `f.write(zapis + '\n')`. – PM 2Ring Jan 13 '17 at 15:47

Ma0 · Answer 2 · 2017-01-13T15:48:10.307

I took the liberty of pythonizing your code a bit.

def unos_knjiga():
    headers = ["Autor", "Naslov", "Godina", "ISNB", "Zanr", "Cena", "Kolicina"]
    print("Podaci za knjigu:")
    knjiga = [input("{}".format(obj + ': ')) for obj in headers]  # see 1
    zapis = '|'.join(knjiga)  # see 2

    print(knjiga)
    print(zapis)

    with open('knjige.txt', 'a') as f:  # see 3
        f.write(zapis + '\n')

    # i guess this is for testing?
    with open("knjige.txt", 'r') as f:
        x = f.read()
    print(x)

    # and this too?
    zapis1 = zapis.split('|')
    print(zapis1)

    # this is not mentioned anywhere
    second_meni()

1) This is a list comprehension. It creates lists by looping through stuff. In this case we are looping through the header list and use its items to construct input statements. The provided input is stored in the list.

2) .join() method. It does what you explicitly did. Joins items from iterators using a string between them.

3) the with keyword. Manages files so that you do not have to. Unless there is a reason not to use it, use it. This was also where the real problem with your code was. You have to use the 'a' mode. 'a' is for append, 'w' is for write. In this context, write means delete everything that was there and write this new stuff. Also note that 'a' mode can also create files, you do not need to temporarily switch to 'w' for that ('r' does not; 'r' is for read).

Cheers!

Thank you. this is a part of my program that i had a problem. Im an epic newbie to this still :/ — Alex, Jan 13 '17 at 15:45
@Alex : the code already add a `\n` that split your books into separate lines. — mootmoot, Jan 13 '17 at 15:46

bonyem · Answer 3 · 2017-01-13T22:55:45.253

I think there are two methods to do this:

FIRST

f = open('knjige.txt','w')

is the piece of code which is responsible for rewriting the existing data in your file. Other option which python offers to append some new data to the existing data is to open a file for writing using append 'a' method. So you can replace your above statement with

f = open('knjige.txt','a')

It won't replace the file with new data you enter.

SECOND

Other option is to open your file in read method, f = open('knjige.txt','r') and copy the existing data to a variable ( variable=f.read('knjige.txt') ). You can also use pickle module and its functions dump and load if you need to maintain your datatype. Now concatenate your new data to the values in 'variable' and again open the file in write method and write it back to it.

score 0 · Answer 4 · answered Jan 13 '17 at 15:38

Your call to open the file, f = open('knjige.txt','w') opens the file, truncating the existing contents should it exist. If you open the file with a mode that appends contents, like a it should not delete previous lines. See https://docs.python.org/2/library/functions.html#open for more information on opening files for reading / writing.

How to save contents of a list to a file?

4 Answers4