Saving/Loading lists in Python

Question

I am new to python (and programming in general) and am making a database/register for a typical class. I wanted the user to be able to add and remove pupils from the database, I used lists primarily for this but have hit a stump.

Whenever I restart the program the list the user has modified returns back to the defualt list I specified in the code. I looked around the internet and tried to save the list onto a seperate txt file. However the txt file also goes back to the defualt every time I restart the program. I would like you to please give me a way to save the changes made to the list and keep them that way. Here is the code (it's not very good):

def menu():
    print "*****************CLASS REGISTER*****************"
    print "Press 1 See The List Of Pupils"
    print "Press 2 To Add New Pupils"
    print "Press 3 To Remove Pupils"
    print "Press 0 To Quit \n"

filename = open('pupil.txt','r')

pupil = ["James Steele", "Blain Krontick", "Leeroy Jenkins", "Tanvir Choudrey"]

def see_list(x):
    print x

def add_pupil(x):
    print "You have chosen to add a new pupil.\n"
    option = raw_input("Please type the childs name.")
    x.append(option)
    filename = open('pupil.txt','w') 
    filename.write('\n'.join(pupil)) 
    filename.close() 
    print option, "has been added to the system."
    return x

def delete_pupil(x):
    print "You have chosen to remove a pupil.\n"
    option = raw_input("Please type the childs name.")
    if option in x:
        x.remove(option)
        filename = open('pupil.txt','w') 
        filename.write('\n'.join(pupil)) 
        filename.close() 
        print option, "has been removed from the system."
    else:
        print "That person is not in the system."
    return x


one = 1
while one != 0:
    menu()
    option = input() 
    if option == 1:
        see_list(pupil)
    elif option == 2:
        add_pupil(pupil)
    elif option == 3:
        delete_pupil(pupil)
    elif option == 0:
        break
    else:
        print "That is not a valible choice."

filename = open('pupil.txt','w') 
filename.write('\n'.join(pupil)) 
filename.close() 


if option == 0:
    quit

By the way, if you want feedback on the code, don't be afraid to use codereview.stackexchange.com — kojiro
– kojiro, Commented May 18, 2012 at 19:51
input() in Python 2 calls eval() which introduce a security issue in your code. If you want numbers consider using int(raw_input()). — rubik
– rubik, Commented May 18, 2012 at 19:54

Tamás · Accepted Answer · 2012-05-18 19:48:08Z

4

Well, you just open the pupil.txt file but never read back its contents. You need something like this:

filename = open('pupil.txt', 'r')
contents = filename.read()
filename.close()

pupil = [name for name in contents.split('\n') if name]

Also, you will need to handle the case when the pupil.txt file does not exist; this can be done with a try..except block around the IO calls.

Finally, as one of the comments has mentioned above, have a look at the pickle module, which lets you store a Python object in a file in Python's internal format (which is not really readable, but saves you a lot of hassle).

answered May 18, 2012 at 19:48

Tamás

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2 Comments

voithos Over a year ago

Or, if it's simple data types (list, dict, etc), you can serialize it as JSON, which is both fast, and (arguably) human-readable.

user1404167 Over a year ago

Ok, thanks, I will look into both pickle and JSON, thanks for the code suggestion.

voithos · Accepted Answer · 2012-05-18 19:50:22Z

1

Not related to your question directly, but this:

one = 1
while one != 0:
    ...

is silly. All you need is:

while True:
    ...

answered May 18, 2012 at 19:50

voithos

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2 Comments

user1404167 Over a year ago

for some reason it does not work for me, is it built in or do you have to define/ assign it.

voithos Over a year ago

Yes, it is built in. It's the constant for "true". The capitalization is important: it's True, not true.

Burhan Khalid · Accepted Answer · 2012-05-18 19:53:10Z

0

This is what a database is for. Use sqlite - a simple file-based database the libraries for which come bundled with python.

answered May 18, 2012 at 19:53

Burhan Khalid

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2 Comments

voithos Over a year ago

Maybe once the application gets more complex, sure... But currently, I think that would be overkill. Since he's new to programming, he probably isn't familiar with SQL anyway.

user1404167 Over a year ago

voithos is correct I am do not know what SQL is but I will check it out once I have experieence in python!

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