Variable scope in python

Data Structures And Algorithms
#1

Hi, I started Python guided path course. In the variable scope section I face an issue.

In the notes we have a code snippet like this

x = "Global Variable" 
def foo(): 
    print("Value of x: ", x) 
foo()

I run it and change the value of variable x here is the code snippet:

x = "Global Variable"
def foo():
    x = "somthig new happen"
    print("Value of x: ", x)
foo()

it work fine without throw any exception it means, we can update the global variable value.
please correct me what I'm missing in understanding the concept.

thanks
#2

Hi, you don’t actually update the global variable. Inside your foo function, you create a brand new x storage. When you have two variables with the same name, one inside a global scope or outer scope in your example it is x = “Global Variable” and one which is inside a function scope or block scope in your example it is x = “something new happen”, this is call a “Variable shadowing”. It’s look like an illusion. You create a global variable x and then you think that i use the same storage inside foo function that i created before, but it is not true. You can try this code snippet.

x = "Global Variable"

def foo():
    x = "Something happen"
    print(id(x))
    print("Value of x: ", x)

print(id(x))
foo()
print(x)

If you really want to change the value of global variable, then you need to do something like this…

x = "Global Variable"

def foo():
    global x
    x = "Something happen"
    print("Value of x inside foo: ", x)

foo()
print("Value of x inside globale : ", x)
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