In short, the question: **Is there a way to prevent Python from looking up variables outside the current scope?**

Details:

Python looks for variable definitions in outer scopes if they are not defined in the current scope. Thus, code like this is liable to break when not being careful during refactoring:

```
def line(x, a, b):
    return a + x * b

a, b = 1, 1
y1 = line(1, a, b)
y2 = line(1, 2, 3)

```

If I renamed the function arguments, but forgot to rename them inside the function body, the code would still run:

```
def line(x, a0, b0):
    return a + x * b  # not an error

a, b = 1, 1
y1 = line(1, a, b)  # correct result by coincidence
y2 = line(1, 2, 3)  # wrong result

```

I know [it is bad practice to shadow names from](https://stackoverflow.com/a/20125739/3005167) outer scopes. But sometimes we do it anyway...

Is there a way to prevent Python from looking up variables outside the current scope? (So that accessing `a` or `b` raises an Error in the second example.)