Saving list data in python

Question

I am wondering how I can save whatever I added to a list when I close a python file. For example, in this "my contact" program that I wrote below, if I add information about 'Jane Doe', what could I do so that next time I open up the same file, Jane Doe still exists.

def main():
    myBook = Book([{"name": 'John Doe', "phone": '123-456-7890', "address": '1000 Constitution Ave'}])
class Book:
    def __init__(self, peoples):
        self.peoples = peoples
        self.main_menu()
    def main_menu(self):
        print('Main Menu')
        print('1. Display Contact Names')
        print('2. Search For Contacts')
        print('3. Edit Contact')
        print('4. New Contact')
        print('5. Remove Contact')
        print('6. Exit')   
        self.selection = input('Enter a # form the menu: ')
        if (self.selection == "1"):
            self.display_names()
        if (self.selection == "2"):
            self.search()
        if (self.selection == "3"):
            self.edit()
        if (self.selection == "4"):
            self.new()
        if (self.selection == "5"):
            self.delete()
        if (self.selection == "6"):
            self.end()
    def display_names(self):
        for people in self.peoples:
                print("Name: " + people["name"])             
        self.main_menu()   
    def search(self):
        searchname = input('What is the name of your contact: ')
        for index in range(len(self.peoples)):
            if (self.peoples[index]["name"] == searchname):
                print("Name: " + self.peoples[index]["name"])
                print("Address: " + self.peoples[index]["address"])
                print("Phone: " + self.peoples[index]["phone"])   
        self.main_menu() 
    def edit(self):
        searchname = input('What is the name of the contact that you want to edit: ')
        for index in range(len(self.peoples)):
            if (self.peoples[index]["name"] == searchname):  
                self.peoples.pop(index)
                name = input('What is your name: ')
                address = input('What is your address: ')
                phone = input('What is your phone number: ')
                self.peoples.append({"name": name, "phone": phone, "address": address})
        self.main_menu()
    def new(self):
        name = input('What is your name: ')
        address = input('What is your address: ')
        phone = input('What is your phone number: ')
        self.peoples.append({"name": name, "phone": phone, "address": address})
        self.main_menu()
    def delete(self):
        searchname = input('What is the name of the contact that you want to delete: ')
        for index in reversed(range(len(self.peoples))):
            if (self.peoples[index]["name"] == searchname):  
                self.peoples.pop(index)

            print(searchname, 'has been removed')
        self.main_menu()   
    def end(self):
        print('Thank you for using the contact book, have a nice day')
        print('Copyright Carson147 2019©, All Rights Reserved')       

main()

A clear and concise segment of code would be much appreciated EDIT: instead of the entire program — Arnav Poddar
– Arnav Poddar, Commented May 27, 2019 at 19:22
docs.python.org/3/library/persistence.html, ... docs.python.org/3/library/csv.html ... docs.python.org/3/library/json.html — wwii
– wwii, Commented May 27, 2019 at 19:24

wwii · Accepted Answer · 2019-05-27 19:28:08Z

3

Use a module from the Data Persistence section of the standard library, or save it as json, or as a csv file.

answered May 27, 2019 at 19:28

community wiki

wwii

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Comments

Alperen Tahta · Accepted Answer · 2019-05-27 19:25:52Z

1

You just convert your list to array inside in function .

np.save('path/to/save', np.array(your_list))

to load :

arr=np.load(''path/to/save.npy').tolist()

I hope it will be helpful

edited May 27, 2019 at 19:25

answered May 27, 2019 at 19:22

Alperen Tahta

4862 silver badges13 bronze badges

3 Comments

Stephen Rauch Over a year ago

And you think the OP is using numpy, why?

Alperen Tahta Over a year ago

To develop myself, can you explain why my solution is bad ?

Stephen Rauch Over a year ago

The OP is very obviously a beginner. Numpy is not really meant for beginners. Throwing numpy into the mix as a way to persist things is going to be confusing for a beginner.

Adam Smith · Accepted Answer · 2019-05-27 19:35:30Z

There are innumerable kinds of serialization options, but a time-tested favorite is JSON. JavaScript Object Notation looks like:

[
    "this",
    "is",
    "a",
    "list",
    "of",
    "strings",
    "with",
    "a",
    {
        "dictionary": "of",
        "values": 4,
        "an": "example"
    },
    "can strings be single-quoted?",
    false,
    "can objects nest?",
    {
        "I": {
            "Think": {
                "They": "can"
            }
        }
    }
]

JSON is widely used, and the Python stdlib has a method of converting objects to and from JSON in the json package.

>>> import json
>>> data = ['a', 'list', 'full', 'of', 'entries']
>>> json.dumps(data)  # dumps will dump to string
["a", "list", "full", "of", "entries"]

You can then save your Book data to json before the program shuts down, and read from json after it starts up.

# at the top
import json
from pathlib import Path

# at the bottom of your program:
if __name__ == '__main__':
    persistence = Path('book.json')
    if persistence.exists():
        with persistence.open() as f:
            data = json.load(f)
    else:
        data = [{"name": 'John Doe', "phone": '123-456-7890', "address": '1000 Constitution Ave'}]

    book = Book(data)
    with persistence.open('w') as f:
        json.dump(f, indent=4)

Arnav Poddar · Accepted Answer · 2019-05-27 19:40:45Z

0

There is no way you can do that without any external modules, such as numpy or pickle. Using pickle, you can do this: (I am assuming you want to save the myBook variable)

import pickle
pickle.dump(myBook, open("foo.bar", "wb")) #where foo is name of file and bar is extension
#also wb is saving type, you can find documentation online

To load:

pickle.load(myBook, open("foo.bar", "rb"))

EDIT:

I was wrong in my first statement. There is a way to save without importing a module. Here is how:

myBook.save(foo.bar) #foo is file name and bar is extention

To load:

myBook=open(foo.bar)

edited May 27, 2019 at 19:40

answered May 27, 2019 at 19:30

Arnav Poddar

3543 silver badges18 bronze badges

2 Comments

Adam Smith Over a year ago

where does the .save method come from? Your edit looks wrong. There definitely is a way to do this without importing a module, but that way is basically "write your own serialization method" which is without a doubt much harder.

Arnav Poddar Over a year ago

I am not 100% sure if it works for lists, but I used it for an image, and it worked perfectly fine

Cireo · Accepted Answer · 2019-05-27 20:42:41Z

As evinced by the many other answers, there are many ways to do this, but I thought it was helpful to have a example.

By changing the top of your file as so, you can use the shelve module.

There are a variety of other things you can fix in your code if you are curious, you could try https://codereview.stackexchange.com/ if you want more feedback.

import shelve

def main():
    default = [
        {'name': 'John Doe', 'phone': '123-456-7890',
         'address': '1000 Constitution Ave'}
    ]
    with Book('foo', default=default) as myBook:
        myBook.main_menu()


class Book:
    def __init__(self, filename, default=None):
        if default is None:
            default = []
        self._db = shelve.open(filename)
        self.people = self._db.setdefault('people', default)

    def __enter__(self):
        return self

    def __exit__(self):
        self._db['people'] = self.people
        self._db.close()

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