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Re: Store a variable permanently

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  Re: Store a variable permanently Jean-Michel Pichavant <jeanmichel@sequans.com> - 2013-03-01 11:19 +0100
    Re: Store a variable permanently Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-02 02:29 +0000

#40244 — Re: Store a variable permanently

----- Original Message -----
> So i have a variable called funds that i want to store the value of
> even after the program is exited. My funds variable holds the total
> value of funds i have. I add a certain number of funds each time i
> run the program by entering how much i want to add. How would i
> store the funds variable to keep its value?
> --
> http://mail.python.org/mailman/listinfo/python-list
> 

Hi,

I would serialize the data.

http://docs.python.org/2/library/pickle.html

funds=5
pickle.dump(funds, 'funds.pickle')

# to reload funds:

funds = pickle.load('funds.pickle')


The good thing with pickle is that it serializes a lot of things, see the "What can be pickled" section of the doc.


JM


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#40311

On Fri, 01 Mar 2013 11:19:22 +0100, Jean-Michel Pichavant wrote:

> ----- Original Message -----
>> So i have a variable called funds that i want to store the value of
>> even after the program is exited. My funds variable holds the total
>> value of funds i have. I add a certain number of funds each time i run
>> the program by entering how much i want to add. How would i store the
>> funds variable to keep its value? --
>> http://mail.python.org/mailman/listinfo/python-list
>> 
>> 
> Hi,
> 
> I would serialize the data.
> 
> http://docs.python.org/2/library/pickle.html


I don't think we should recommend to a newbie that they use pickle 
without even warning them that using pickle is insecure and dangerous if 
they are opening pickles from untrusted sources.

But for a single int, pickle too is overkill, and a simple human-readable 
and writable file is probably all that is needed:

def save_value(n, configfile='myconfig'):
    if n != int(n):
        raise ValueError('expected an int')
    with open(configfile, 'w') as f:
        f.write("value=%d" % n)

def load_value(configfile='myconfig'):
    with open(configfile) as f:
        s = f.read().strip()
    a, b = s.split("=", 1)
    if a.strip() != "value":
        raise ValueError('invalid config file')
    return int(b)


Untested but ought to work.


-- 
Steven

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