Which is the correct use of global variables in Python 3?:
1) Stating global VAR_NAME
once in the core script (not within a function) and then simply referring to the variable as VAR_NAME
everywhere else
2) Stating global VAR_NAME
once within every function that uses the global variable and then simply referring to the variable as VAR_NAME
for the rest of the function and within the core script itself
In the first case the global keyword is pointless, so that is not correct. Defining a variable on the module level makes it a global variable, you don't need the global keyword.
The second example is correct usage.
However, the most common usage for global variables are without using the global keyword anywhere. The global keyword is needed only if you want to reassign the global variables in the function/method.