Save and Overwrite Variables in Python

Question

I need a little bit of help on overwriting python variables. Here's the best example I could give. IF someone opens up my program (in .exe or .py) and this were to come up:

var = 5
var = raw_input("Enter the new variable value: ") ##THE PERSON ENTERS 3
var = 3

Now, the user closes the file/program, next time they open it, they want the program to remember that var = 3, so it overwrote the var = 5 with var = 3. I don't know if this is possible, but if it is, could you let me know?

To Clarify: I want my .py or .exe to remember that a variable was changed, and overwrite the old variable with the new one, so the next time they open the file, the variable is already changed.

You want to use file I/O, and explicitly write and read settings like these. Read a decent Python tutorial for beginners first though. — Martijn Pieters
– Martijn Pieters, Commented Feb 12, 2013 at 18:36
I would suggest you progress a bit further in whatever python tutorial it is you're following. What you're looking to do is something called persistence, and there's a fair bit of basics ahead of you before you hit the parts about persistence. — JosefAssad
– JosefAssad, Commented Feb 12, 2013 at 18:38
@Jordan Do you want the PROGRAM or any OTHER FILE to keep the change ? If first case, the program will have to change it's own file, I beg it's possible but it will need some skills. If second case, it's persistence — eyquem
– eyquem, Commented Feb 12, 2013 at 20:24

phihag · Accepted Answer · 2013-02-12 19:08:03Z

4

You'll need to somehow store the value, for example in a file, database, or with some service.

For example, using a simple file:

import io,os
try:
    with io.open('~/.jordan_last_value', 'r', encoding='utf-8') as f:
        var = f.read()
except IOError: # Read failed
    var = raw_input('Enter the new variable value')

    # Save value to disk
    with io.open('~/.jordan_last_value', 'w', encoding='utf-8') as f:
       f.write(var)

print ('Current value is ' + var)

As you can see, this can be somewhat complex, so you may want to refresh your knowledge of file handling. Also, this example code can just store strings.

If you want to be able to store more complex objects, you'll need a way to transform them from and to bytestrings first. Have a look at the json or pickle modules for that.

edited Feb 12, 2013 at 19:08

answered Feb 12, 2013 at 18:39

phihag

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swietyy · Accepted Answer · 2013-02-12 18:37:56Z

2

You can use pickle module, json or whatever :P

answered Feb 12, 2013 at 18:37

swietyy

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1 Comment

JosefAssad Over a year ago

Not a fan of giving people answers that are only literally correct and don't account for context. The context here in my opinion is the asker is missing a lot of programming basics and will just get frustrated jumping ahead to using a module like pickle. The asker's challenge is pedagogical in nature and not technical.

Rushy Panchal · Accepted Answer · 2013-02-12 19:42:04Z

0

Using the pickle module:

import pickle
try: # try to open the file
    with open('jordan_data.pkl', 'r+') as f:
        var = pickle.load(f)
except IOError: # if it doesn't exist, get new input
    var = raw_input("Enter the new variable value: ") # THE PERSON ENTERS 3
    with open('jordan_data.pkl', 'a+') as f: # 'a' will create the file if it doesn't exist
        pickle.dump(var, f) # then, save the file

edited Feb 12, 2013 at 19:42

answered Feb 12, 2013 at 18:57

Rushy Panchal

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1 Comment

phihag Over a year ago

You don't need close - the with statement does that already. Additionally, you should open the file in binary mode. Also, the renaming of pickle makes it unnecessarily hard to understand the code.

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