How to Make a Local Variable (Inside a Function) Global

How to make a local variable (inside a function) global

Here are two methods to achieve the same thing:

Using parameters and return (recommended)

def other_function(parameter):
    return parameter + 5

def main_function():
    x = 10
    print(x)    
    x = other_function(x)
    print(x)

When you run main_function, you'll get the following output

>>> 10
>>> 15

Using globals (never do this)

x = 0   # The initial value of x, with global scope

def other_function():
    global x
    x = x + 5

def main_function():
    print(x)    # Just printing - no need to declare global yet
    global x   # So we can change the global x
    x = 10
    print(x)
    other_function()
    print(x)

Now you will get:

>>> 0    # Initial global value
>>> 10   # Now we've set it to 10 in `main_function()`
>>> 15   # Now we've added 5 in `other_function()`

Using global variables in a function

You can use a global variable within other functions by declaring it as global within each function that assigns a value to it:

globvar = 0

def set_globvar_to_one():
    global globvar    # Needed to modify global copy of globvar
    globvar = 1

def print_globvar():
    print(globvar)     # No need for global declaration to read value of globvar

set_globvar_to_one()
print_globvar()       # Prints 1

Since it's unclear whether globvar = 1 is creating a local variable or changing a global variable, Python defaults to creating a local variable, and makes you explicitly choose the other behavior with the global keyword.

See other answers if you want to share a global variable across modules.

How to declare global variable inside function?

You have two problems:

1. main is not a loop. It's a function.

2. Your function syntax is wrong. You need to have parentheses after the function name. Either of these are valid syntaxes for main:

    int main() {
    }
   
    int main(int argc, const char* argv[]) {
    }
   

Then, you can declare a local variable inside main like so:

int main() {
  int local_variable = 0;
}

or assign to a global variable like so:

int global_variable;

int main() {
  global_variable = 0;
}

How to make a local variable into a global in JavaScript

You can do the following to access a global inside of a function.

Any variable created outside the scope of a function can be referenced inside of a function.

Var myGlobalVar;

Function myFunction(){
   if(....) {
        myGlobalVar = 1;
   }
}

Python: Change: How do I make local variable global?

Use the global keyword

# Hello World program in Python

def foo():
    global bar #Define the global variable bar
    bar = "Hello world" #Set bar to hello world

foo() #Set bar
print bar #Hello world

#Second example

fo = "Initial value" #Initial value

def foobar():
    global fo
    fo = "Value changed"
    bar = "Value changed" #Global variable 'bar' isn't changed because we didn't declare bar global in this function. There is only a local variable named 'bar' created.

print fo #Initial value
print bar #Hello world

foobar() #Change value

print fo #Value changed
print bar #Hello world

http://tpcg.io/yUvZD8 (Try it out)

Never make a variable global, just declare it global at the beginning of the function and change the value.

global variable inside main function python

A variable created inside a method (e.g., main) is local by definition. However, you can create a global variable outside the method, and access and change its value from side any other method.

To change its value use the global keyword.

How do I change the value of a global variable inside of a function

Just reference the variable inside the function; no magic, just use it's name. If it's been created globally, then you'll be updating the global variable.

You can override this behaviour by declaring it locally using var, but if you don't use var, then a variable name used in a function will be global if that variable has been declared globally.

That's why it's considered best practice to always declare your variables explicitly with var. Because if you forget it, you can start messing with globals by accident. It's an easy mistake to make. But in your case, this turn around and becomes an easy answer to your question.

Python function global variables?

If you want to simply access a global variable you just use its name. However to change its value you need to use the global keyword.

E.g.

global someVar
someVar = 55

This would change the value of the global variable to 55. Otherwise it would just assign 55 to a local variable.

The order of function definition listings doesn't matter (assuming they don't refer to each other in some way), the order they are called does.

---

Related Topics