Accessing python variable outside function scope when reassigning to update variable-CodePudding

I want to keep track of the current max of a calculated cosine similarity score. However, I keep getting the error UnboundLocalError: cannot access local variable 'current_max_cosine_similarity_score' where it is not associated with a value

In Javascript, I can typically do this without a problem using the let keyword when working with a variable outside of a function scope. However, in Python that doesn't seem to be the case.

What would be the pythonic way of going about this?

current_max_cosine_similarity_score = -math.inf

def func(acc, v):
  calculated_cosine_similarity_score = ...

  if calculated_cosine_similarity_score > current_max_cosine_similarity_score:
    current_max_cosine_similarity_score = max([current_max_cosine_similarity_score, calculated_cosine_similarity_score])
    
    acc['cosineSimilarityScore'] = calculated_cosine_similarity_score
  
  return acc


print(reduce(func, [...], {}))

CodePudding user response：

You have to declare current_max_cosine_similarity_score as global (or nonlocal) in func(). But that's nevertheless a bad idea. The "pythonic" way would be to use a generator, closure or a class with a get_current_maximum().

Probably the most "pythonic" closure solves your problem:

from functools import reduce

def calc_closure():
    def _calc(value, element):
        # do calculations on element here
        if element > value:
            _calc.current_max_value = element
        return _calc.current_max_value 
    # using an attribute makes current_max_value accessible from outer
    _calc.current_max_value = -np.math.inf
    return _calc

closure_1 = calc_closure()
closure_2 = calc_closure()

print(reduce(closure_1, [1, 2, 3, 4, 1]))
print(closure_1.current_max_value )
print(closure_2.current_max_value )

Output:
4
4
-inf