Global and Local Variables in Python
Global variables are the one that is defined and declared outside a function and we need to use them inside a function.
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The variable s is defined as the string “I love Geeksforgeeks” before we call the function f(). The only statement in f() is the “print s” statement. As there are no locals, the value from the globals will be used.
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If a variable with the same name is defined inside the scope of function as well then it will print the value given inside the function only and not the global value.
The question is, what will happen if we change the value of s inside of the function f()? Will it affect the globals as well? We test it in the following piece of code:
Line 2: undefined: Error: local variable 's' referenced before assignment
To make the above program work, we need to use the “global” keyword. We only need to use the global keyword in a function if we want to do assignments / change them. global is not needed for printing and accessing. Why? Python “assumes” that we want a local variable due to the assignment to s inside of f(), so the first print statement throws this error message. Any variable which is changed or created inside of a function is local if it hasn’t been declared as a global variable. To tell Python, that we want to use the global variable, we have to use the keyword “global”, as can be seen in the following example:
Now there is no ambiguity.
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A Good Example
global : 1 Inside f() : 1 global : 1 Inside g() : 2 global : 1 Inside h() : 3 global : 3
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