Local and Global

Scope is the region of a program where a name can be seen. A variable created inside a function is local to it. It is born when the function is called and it dies when the function returns. Code outside the function cannot see it at all.

A variable created at the top level of a file is global. Every function in that file can read it.

Local scope

PYTHON

def greet():
    message = "Akwaaba"
    print(message)

greet()
print(message)  # NameError

JAVASCRIPT

function greet() {
  let message = "Akwaaba";
  console.log(message);
}

greet();
console.log(message); // ReferenceError

Compare → Both languages agree completely here. `message` exists only inside `greet`. Asking for it outside is an error in Python and in JavaScript. The wording of the error differs, the rule does not.

EXAMPLE

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YOUR TURN

Your turn → Now add print(message) as the last line and run it again. Read the error carefully, it is telling you exactly what scope means.

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Syntax has to be exact. Every quote, bracket and parenthesis needs its partner, and in Python the spaces at the start of a line count. One slip and the program won't run; the message will say where.

✦ Why this is a feature, not an obstacle

Local scope means you can name a variable `total` inside twenty different functions and none of them collide. Without it, every name in a large program would have to be unique. Scope is what makes code composable.

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