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Python

Keyan Abtahi
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Keyan Abtahi
Python Web Development Techdegree Student 267 Points

Basic VAR question: How do I use a local var in a function without global?

Hi!

I keep having the same problem whenever I write code. I can't seem to figure out how to use the vars outside of a function inside a functions scope.

Google tells me to "You can use global but DONT use global", or only complex examples I dont fully grasp yet.

  • If I try to use a var that is outside of a functions scope, I get an error.
  • If I move said var to the functions scope and make it local, the function works BUT the rest of the code where that local var is used creates errors.

If I have to use the same vars in different functions, do I have to declare them in every single function? Can I pass vars from one function to another function??

Can someone explain to me like I'm 5? Thank you!

6 Answers

I had to look up the syntax -- it looks like you need to structure the "return" syntax a little differently for Python, but I think this is how you'd do it:

def doStuff():
  thing1 = "Hello"
  thing2 = "Good Bye"
  return { "thing1": thing1, "thing2": thing2 }


doStuffVariables = doStuff()


print(doStuffVariables["thing1"])
print(doStuffVariables["thing2"])

print(doStuffVariables)

Cheers, Keyan, and good luck to you!

Hey Keyan, Your suspicions are right, you don't want to re-declare the same variables over and over in every function. I'll try to keep it simple. If you have variables that are outside of a function, and you want to use them inside the function, the easiest way to do that is to pass them into the function as arguments. That looks like this:

// Here is your global variable:

var whatever = "This variable is outside the function, in the global scope.";

// Here is the function definition, which establishes that the function can take an argument ["arg"]:

function doStuff(arg) {
  alert(arg); // This just pops up an alert modal with whatever the value of the argument is.
}

// Now when you actually call (execute) the function, if you pass in the global variable, the function will use it!:

doStuff(whatever); // should alert "This variable is outside the function..."

You can pass in as many arguments as you want:

function doStuff(arg1, arg2, arg3) {
  // and now you can do anything you want with any of those passed-in variables:
  console.log(arg1);
  alert(arg2);
  var newThing = parseInt(arg3, 10) * 5;
  return arg1 + " " + arg2;
}

doStuff("Hello", "Woohoo!", 7);

And while it's true that it's better not to leave a bunch of stuff in the global scope, it's totally fine for small websites and totally fine when you're still learning the basics. You don't need to over-optimize when you're still learning the basic concepts.

Hope that helps you! Let me know if it's still not making sense.

Whoops, I had JavaScript on the brain, but I just saw you flagged this as a Python question. Luckily, the exact same concept holds true, you just need new syntax:

whatever = "This variable is outside the function"

def doStuff(arg):
  print(arg)

doStuff(whatever)

Make sense?

The only way to get things out of a function is to "return" them, and a function can only return 1 single "thing" - that's how functions work. So, if you want to return several variables/values out of a function to use elsewhere, you have to collect them into an object first, and then return that object. Then you have to assign that returned object as the value of a new variable that's in the global scope.

It's probably easier to understand in an example (I'm using JavaScript again since I know that syntax better - again, the concept is the same in Python and other languages):

function doStuff() {

  // Here are some variables inside a function:

  var thing1 = "Hello";
  var thing2 = "Good Bye";

  // To get them out of the function, create an object (using curly braces) with the variables in it, and have that be what the function returns:

  return {
    thing1,
    thing2
  }
}

// Now call (execute) the function to get the variables out to a new variable (doStuffVariables) in the global scope:

var doStuffVariables = doStuff();

// Now you can use them! doStuffVariables is an object and thing1/thing2 are properties, with "Hello" and "Good Bye" as their values.

console.log( doStuffVariables.thing1 ); // logs "Hello"
console.log( doStuffVariables.thing2 ); // logs "Good Bye"

// And if you want to see all your variables and their values (for debugging etc):

console.log( doStuffVariables );

Hope all that makes sense again!

Keyan Abtahi
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Keyan Abtahi
Python Web Development Techdegree Student 267 Points

Hi again Eric! The way you explain things are very helpful, I do understand the concept behind what you just taught me.

The issue is the error I get: AttributeError 'set' object has no attribute 'bet'

The code I use is: https://pastebin.com/vMEmB7ZP

Your code works in JS though, perfectly and exactly like I want it to, so it has to be Python related..

Thank you once again for your time and replies!

Keyan Abtahi
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.a{fill-rule:evenodd;}techdegree
Keyan Abtahi
Python Web Development Techdegree Student 267 Points

Eric - thank you so much. I can't thank you enough for your time and effort! I finally learned how to do this - it's been holding me.back.immensely! Thank you!

Keyan Abtahi
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.a{fill-rule:evenodd;}techdegree
Keyan Abtahi
Python Web Development Techdegree Student 267 Points

Hello Eric, thank you for your reply! That makes sense, your example is great!

A last question regarding this is, what if its reversed? What if you want to take something defined in a functions scope and use it outside the said function?

E.g: https://pastebin.com/J17xF2FU

Thank you!