How do I set variables in functions and access them outside of the function in Python?

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My Code:

import time
import sys
authenticating="authenticating"
check_verification="verifying username and password......"



#sets player username and password
print "Welcome to the game."
def set_player_credentials():
    player_username=raw_input("Set username:")
    player_password=raw_input("Set password:")
    for x in check_verification:
        sys.stdout.write(x)
        sys.stdout.flush()
        time.sleep(0.1)
    print "Login Set."
    time.sleep(0.5)



#login screen
print "Username: %s" % (player_username)
print "Password: %s" % (player_password)
check_credentials=raw_input("Is this correct? Y/N")
if check_credentials=="Y" or check_credentials=="y" or check_credentials=="Yes" or check_credentials=="yes":
    print "End of my program for now"
elif check_credentials=="N" or check_credentials=="n" or check_credentials=="No" or check_credentials=="no":
    set_player_credentials()

When I run this code, I get the error:
Traceback (most recent call last):
File "/home/ubuntu/workspace/Game.py", line 23, in <module>
print "Username: %s" % (player_username)
NameError: name 'player_username' is not defined

I want to be able to set the variable whenever I want by calling the set_player_credentials function. How do I do this? Thanks for the help!

Posted 6-Mar-15 18:33pm

Blake Allen

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Sergey Alexandrovich Kryukov 7-Mar-15 0:43am

The question is: why? This is not how programming works. Accessing a local from outer scope makes no sense, not needed, useless, impossible, wrong idea. You need to start learning programming in general. Right, basic things: functions, variables, types and instances...

By the way, what do you think your tag "globalization" means? :-)

—SA

Blake Allen 7-Mar-15 0:46am

I have completed the whole python programming course on codecademy.com. What do you mean this is not how programming works? What should I do instead to be able to set the variable player_username and player_password whenever I want without having to type it out?

Sergey Alexandrovich Kryukov 7-Mar-15 1:02am

You need to formulate you ultimate goal, not "be able to set the variable..." and the like.

1) you cannot use undefined variables; 2) even if you define one, you cannot use it outside its scope; not only it's impossible, it also makes no sense.

Do you seriously think that you can impress anyone by completion of computer course? Too many people here knows well that it means nothing. Especially after your clear demonstration of having no clue on the very basics. At this moment, your knowledge is not zero, it's much less: false knowledge. The sooner you realize it, the better. After a while, you will smite at yourself. Not to worry, it's not hard to learn with time. Especially if you start trusting logic and your own brain, instead of trusting courses. Please, no offense. Believe me, we only want to help you.

—SA

Blake Allen 7-Mar-15 1:12am

Okay, thank you for telling me how experienced I am. Now is there any way to set the player's username/password and change it quickly without having to type out the whole code again?

Sergey Alexandrovich Kryukov 7-Mar-15 1:18am

Oh, just please don't get offended...

Look, this is called authentication. It is done only once. No need not only to type it again, but even to check again. You check up if it passes, and them either exit game or continue, and forget the variable.

More seriously, you hardly really need authentication at all. Why? And how you do it? Compare the name with name, password with password?

—SA

Blake Allen 7-Mar-15 1:25am

I'm in the process of making a game, where if they close the game it will save their progress. Therefore, it will matter what their username and password is later on. I won't get into the details right now. Do you know how to do what I asked? And yes, it is true that I am a beginner. But I do understand general concepts such as variables and functions.

Blake Allen 7-Mar-15 1:27am

And maybe I doing this completely wrong or something. Can you explain what I should do instead please?

Sergey Alexandrovich Kryukov 7-Mar-15 2:02am

You did not answer how you use passwords. I mean, it could be as unsafe as not having any.

You are doing completely wrong, but it's the matter of some code design. You can only access objects from outer scope. You can define variable in outer scope, or you can define the type encapsulating the data, initialize it and pass its only instance where it has to be used.

—SA

Blake Allen 7-Mar-15 2:06am

okay, that makes sense. Thank you. So just to clarify, there is no way to declare a variable inside a function and access it anywhere else that isn't in the same scope. Is this correct?

Sergey Alexandrovich Kryukov 7-Mar-15 2:25am

It needs more understanding...
Those variables simply don't exist between calls, even though nobody "deletes" them. They are stored on stack, and the stack frame is removed, its memory reused. You need to understand stack operation as one of the fundamentals. On high-level languages, you never operate call stack directly, but real understanding of local variables, method parameters and calls/returns (and also exceptions) is impossible without understanding of what happens with the stack. I hope you can understand such things: a pure black-box description can be way too complex compared to looking under the hood...
—SA

Blake Allen 7-Mar-15 2:36am

Okay, I googled stack and understand it now. I also understand why I can't get the variable outside the function now. Thanks for your help and for not getting too pissed at my ignorance xD.

Sergey Alexandrovich Kryukov 7-Mar-15 2:51am

No problem at all, always glad to help. Perhaps I'll put some formal answer to have the topic closed.
You may want to accept it formally, and it won't prevent you from asking follow-up questions and getting other answers.
—SA

Blake Allen 7-Mar-15 2:02am

And if a completion of a tutorial "means nothing", then what should I do to learn to program in python?

Sergey Alexandrovich Kryukov 7-Mar-15 2:05am

I did not say "tutorials mean nothing". You can read again and see what I've said, but please don't put different words in my mouth.

"To learn code?" What is that? You need to learn programming, software development, computer science... To learn? A lot; not a matter of short question.
Read this first: http://norvig.com/21-days.html.

—SA

Blake Allen 7-Mar-15 2:14am

okay, sorry for changing your words. I meant to say "the completion of a tutorial means nothing."

And at the moment I just want to learn to program in Python.

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Sergey Alexandrovich Kryukov · Accepted Answer · 2015-03-06T20:56:00

Let me summarize:

You have to 1) define variables, 2) if the variable is defined, it cannot be used in outer scope. Not only it is impossible, but it makes no sense. Such variables are stored on the call stack and simply don't exist between calls, its memory is re-used after the frame stack is removed.

You can declare variable on outer scope, but this practice is very questionable. First, you should better encapsulate related data in classes, create class instance and pass them be reference where they need to be used.

And, as to the education, training, knowledge… Everyone needs to read this, first of all:
Peter Norvig, Teach Yourself Programming in Ten Years,
http://norvig.com/21-days.html[^].

Very encouraging, isn't it? :-)

Which you the best of luck.

—SA

Richard MacCutchan · Accepted Answer · 2015-03-06T22:28:00

You could use basic file I/O to store your details, see https://docs.python.org/3.3/library/csv.html[^] for one possible way. Remember though that the content of a .csv file will not be secure, as it is simple text, so anyone can read it. For proper security you should use some form of database, but that is a more advanced topic.

How do I set variables in functions and access them outside of the function in Python?

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