access to variables of enclosing function in python

Question

I want to write a function which returns itself a function.

from types import FunctionType
import numpy as np    

def outer_function(beta: np.array, K: np.array, increment: str,
                   augmented: bool, prior: FunctionType=None, **kwargs) -> FunctionType:
            
        def g(x: float) -> float:
            if prior is None:
                prior = x**2
            return beta+x+prior
        return g

The problem I'm encountering is that certain variables of the outer function are not in the scope of the inner, while others are

 test = outer_function(np.array(0), np.array([1,2,3]), increment="hello", augmented=False, prior=None, alpha=10)

 In [91]: pdb.runcall(test, 10)
> <ipython-input-87-16d13c025c81>(5)g()
-> if prior is None:
(Pdb) print(prior)
*** NameError: name 'prior' is not defined
(Pdb) dir()
['beta', 'x']
(Pdb) print(x)
10
(Pdb)

as you can see I only get the variable x and beta. But all the other variables are not seen by g. How can I make all variables of the outer accessible for the inner?

I'm sure that you would have seen the error: UnboundLocalError: local variable 'prior' referenced before assignment before you started debugging. If you had searched for that you would have seen answers on stackoverflow. — quamrana
– quamrana, Commented Aug 28, 2021 at 11:05

Iain Shelvington · Accepted Answer · 2021-08-28 10:47:14Z

2

The Python compiler detects prior = in the g function and assumes that "prior" is a local variable, you need to tell the compiler that you want to access it from the outer function/scope using nonlocal

    def g(x: float) -> float:
        nonlocal prior
        if prior is None:
            prior = x**2
        return beta+x+prior

answered Aug 28, 2021 at 10:47

Iain Shelvington

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quamrana · Accepted Answer · 2021-08-28 10:46:51Z

1

Its because you are possibly reassigning prior. The python compiler marks prior as local because of that (and ignores the parameter to outer_function)

Here is one fix:

def outer_function(beta: np.array, K: np.array, increment: str,
                   augmented: bool, prior: FunctionType=None, **kwargs) -> FunctionType:
            
        def g(x: float) -> float:
            p = prior
            if p is None:
                p = x**2     # reassign to p
            return beta + x + p
        return g

answered Aug 28, 2021 at 10:46

quamrana

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