Global Variable Reference inside a function

Question

I'm trying to reference a global variable inside a function. This function is being defined in a separate file and imported into the main file and applied to a dataset. Here's code:

def to_nominal(dataset):
    global ngdp
    global gdp_deflator_series
    
    bools = []
    for date in ngdp.Date:
        if date in set(dataset.Date).intersection(set(ngdp.Date)):
            bools.append(True)
        else: bools.append(False)
    
    npci_deflator_series = gdp_deflator_series[bools].reset_index(drop = True)
    
    bools = []
    for date in dataset.Date:
        if date in set(dataset.Date).intersection(set(ngdp.Date)):
            bools.append(True)
        else: bools.append(False)
        
    dataset_bools = dataset[bools]
    dataset = dataset_bools.reset_index(drop = True).drop(['YEAR', 'QUARTER', 'Date'], axis = 1).mul(npci_deflator_series, axis =0)
    dataset['Date'] = dataset_bools.Date
    return dataset

I throws the error: 'ngdp' not defined. Initially I though this was because I had to specify that ngdp was a global variable, but the problem seems to persist. I think it might have to do with the fact that i'm importing the function into another file? Any thoughts will be appreciated.

Answer 1

From your description, it sounds like this function is being defined in module A , and imported into another module, B , that has ngdp in it's own globals, and you want A.to_nominal to make use of B.ngdp .

That's not possible. Global scope is tied to the module where the function is defined; even when you import the function into another module, it still looks for globals in the original module's ( A ) scope.

You need to either define both the global and the function in the same module (the simplest approach), or tie them together in some other way (ideally not via a circular import, with A importing ngdp , while B imports to_nominal , because that's error-prone as all get out). If they can't be in the same module, simply passing ngdp as an argument to to_nominal would be a reasonable solution.