[Tutor] Help with basic user-data file

Liam Clarke ml.cyresse at gmail.com
Fri Oct 13 08:46:33 CEST 2006

Hi Asrarahmed,

There's a few questions in there, and unfortunately I don't have a copy 
of your book. But I'll try to answer them, and I'll change the order so 
that they build on each other.

 >I am not sure of using time function in python..

Depending on what you're trying to do, the simplest way is to just use 
the datetime module. http://docs.python.org/lib/module-datetime.html

 >>> import datetime
 >>> the_time_right_now = datetime.datetime.now()

This creates a datetime object. You can do all sorts of useful stuff 
with them, but for now, you probably just want to display the time. You 
can just

 >>> print the_time_right_now
2006-10-13 19:26:45.671000

But that may not be the most useful format. Datetime objects have a 
method called strftime(), and you can give it format strings as per the 
time module -
http://docs.python.org/lib/module-time.html to change the output. For 

 >>> print the_time_right_now
2006-10-13 19:26:45.671000

 >>> print the_time_now.strftime("%I:%M%p, %A %d %B %Y")
07:26PM, Friday 13 October 2006

In that case in the format string %I means hours in 1-12 format, %M is 
minutes, %p is AM/PM, %A is the full name of the day, %d is the day 
number, %B is the full month name and %Y is the full year.'

Have a play with it.
> I am trying to modify the userManagement program given in Core Python 
> Programming. It uses a dictionary to store user-password information. 
> The usernames are the keys and the passwords are the values.
> Now I want is to add a third element; last login time.

Okay. So what could do here is instead of having the password as a 
value, have a list or a dictionary as the value and store the password 
and login time in that.

For example:

 >>> userInfo = {}
 >>> userInfo['Liam'] = { 'password' : 'snooze', 'last_login_time': 

If you print userInfo, you'll see that it's saved a datetime object in 
 >>> print userInfo
{'Liam': {'password': 'snooze', 'last_login_time': 
datetime.datetime(2006, 10, 13, 19, 34, 58, 437000)}}

You could then retrieve my password by

 >>> print userInfo['Liam']['password']

Or the datetime object you created with
 >>> print userInfo['Liam']['last_login_time']
2006-10-13 19:34:58.437000

> I want to store this information in a file so that the data is not 
> lost once the program stops execution.
You'd need to use the pickle module. (Or cPickle, which is marginally 
faster. They work the same, more or less)

 >>> import pickle

Pickle will turn objects into a stream of bytes, which you can save to a 
file. You can then reopen the file, and reload the objects.
So, once you've imported pickle, you need to open a file to write to. 
Make sure you open it in binary mode (So file mode will be "wb")

 >>> save_file = open("userInfo.pck", "wb")

You then use the pickle.dump() method to serialize the object -

 >>> pickle.dump(userInfo, save_file)

Make sure you close the file afterwards.

 >>> save_file.close()

Now, next time you start up -

 >>> import pickle

You use the pickle.load() method to get your object back. First thing is 
to open the file you saved it to, (open it in binary mode).

 >>> load_file = open("userInfo.pck", "rb")
 >>> userInfo = pickle.load(load_file)
 >>> load_file.close()
 >>> print userInfo
{'Liam': {'password': 'snooze', 'last_login_time': 
datetime.datetime(2006, 10, 13, 19, 34, 58, 437000)}}

Hope that helps.


Liam Clarke

More information about the Tutor mailing list