How to store dictionary data over multiple uses?

Question

I am creating a login script and I store the usernames and passwords in a dictionary. The problem is though, when I open it a second time it doesn't store the users that have already been registered. I know this is normal but is there a way to get round that? Perhaps using a file?

Here is my EDITED code:

import os
import sys
users={}
status=""

def login():
    status=raw_input("Are you a new user?")
    if status=="y"
        createnewuser=raw_input("Create username: ")
        if createnewuser in users:
            print "User already exists!"
        else createpsswrd=raw_input("Create new password")
            users[createnewuser]=createpsswrd 
            print "Register successful!"
    elif status == "n":
        login=raw_input("Username: ")
        passw=raw_input("Password: ")
        if login in users and users[login]==passw:
            print "Login successful!"
            os.system("python file.py")
            return
        else:
            print "Username and password do not match."
try:
    with open('file') as infile:
        cPickle.load(infile)
except:
    users = {}

while status != "q":
    login()

with open('file') as outfile:
    cPickle.dump(users, outfile)

Edited results: I get through the entire script with no errors but the outfile file has nothing written on it. The dictionary still doesn't save across sessions so nothing has changed. I have changed all my sys.exit()'s to returns as well. I am using Raspian on a raspberry Pi 2 if that matters.

EDIT 2

Answered by me below :)

See this http://stackoverflow.com/questions/1229068/with-python-can-i-keep-a-persistent-dictionary-and-modify-it — Sameer Naik, Sep 16 '15 at 07:22
You'll have to serialize and reload data on each run. Take a look as [docs](https://docs.python.org/2/library/persistence.html), especially [pickle](https://docs.python.org/2/library/pickle.html) module. — Łukasz Rogalski, Sep 16 '15 at 07:22
Also, kill that `sys.exit()`. That's going to throw off any external program flow you later come up with. Use a `return` to break out of a function, instead — inspectorG4dget, Sep 16 '15 at 07:50

inspectorG4dget · Answer 1 · 2015-09-16T07:31:16.503

3

You are looking for a way to serialize your information. Python has the builtin cPickle library for this:

import cPickle

try:
    with open('/path/to/file') as infile:
        users = cPickle.load(infile)
except:
    users = {}

while status != "q":
    login()

with open('/path/to/file', 'w') as outfile:
    cPickle.dump(users, outfile)

edited Sep 16 '15 at 07:31

answered Sep 16 '15 at 07:23

inspectorG4dget

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I assume "path to file" is my original file that I wrote above? – Jonah Fleming Sep 16 '15 at 07:30
@JonahFleming: nope! it's the file to which you want to save your data – inspectorG4dget Sep 16 '15 at 07:31
So I write it in my original file? – Jonah Fleming Sep 16 '15 at 07:33
yes. Replace your while-loop with the `login()`, with my code – inspectorG4dget Sep 16 '15 at 07:34
I t doesn't work. Nothing gets written to the file I specified. No error either. – Jonah Fleming Sep 16 '15 at 07:38
Check to make sure that there's something in your dictionary before you write it out; i.e. `print users` before you save it – inspectorG4dget Sep 16 '15 at 07:39
Doesn't my new user statement write it to the dictionary? – Jonah Fleming Sep 16 '15 at 07:45
Also printing users would show the user, usernames and passwords. – Jonah Fleming Sep 16 '15 at 07:46
@JonahFleming: I meant print it now, for diagnostic purposes – inspectorG4dget Sep 16 '15 at 07:46
@JonahFlemingL Please edit your original post to show your current code, the input with which you tested it, and the observed output – inspectorG4dget Sep 16 '15 at 07:53
@JonahFleming: I left a comment on your question. You should address that as well – inspectorG4dget Sep 16 '15 at 15:22
I still need help pls! – Jonah Fleming Sep 16 '15 at 22:31
@JonahFleming: I'm waiting for you in chat – inspectorG4dget Sep 16 '15 at 23:12
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/89956/discussion-between-inspectorg4dget-and-jonah-fleming). – inspectorG4dget Sep 17 '15 at 19:20

score 0 · Accepted Answer · answered Sep 17 '15 at 06:12

Ok, by talking to someone at my school I worked out the answer. Here is the code working. Comments in the script explain:

import os
import sys
import pickle
#'users' dictionary stores registed users and their passwords.
status=""
users={}

#loads pickled data
def loadUsers():
    global users
    users=pickle.load(open("Dump.txt", "rb"))
#saves pickled data to Dump.txt
def saveUsers():
    global users
    pickle.dump(users, open("Dump.txt", "wb"))
#login() can register people and login.
def login():

      global users
      status=raw_input("Are you a new user y/n? Press q to quit. ")
      #creates new user by adding username and password to 'users' dictionary
      if status == "y":
            createNewUser=raw_input("Create username: ")
            if createNewUser in users:
                  print "User already exists!"
            else:
                  createPsswrd=raw_input("Create new password: ")
                  users[createNewUser] = createPsswrd
                  print "Register succesful!"
      #logs in registered users by checking for them in 'users' dictionary     
      elif status == "n":
            login=raw_input("Username: ")
            passw=raw_input("Password: ")
            if login in users and users[login] == passw:
                  print "Login successful!"
                  #opens protected app/file 
                  os.system('python Basketball\ Stats.py')
            else:
                  print "Username and password do not match!"
      #returns status to main body of script 
      return status

loadUsers()
#quit and save
try:
    while status != "q":
                    status = login()
except Exception as e:
    raise
finally:
    saveUsers()

Thanks to @inspectorG4dget for giving me the tools to work on!

How to store dictionary data over multiple uses?

2 Answers2