Scope of variables in function factories

I was wondering about the scope of the variable a in the following Python snippet,

# ============================
def get_plotter():
    def get_a():
        return a
    a = 3.14
    return get_a
# ============================
if __name__ == '__main__':
    f = get_plotter()
    print f()
# ============================

The output is 3.14 , but looking at the code I would have expected a to go out of scope as soon as get_plotter() terminates, effectively leaving an undefined something.

Is it just volatile memory contents that are printed here? What's going on?

---

This works because of closures, or "functions with data attached", and is explained well here

https://stackoverflow.com/a/141426/735204

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