If you were doing this:
model._meta.get_field('g').get_internal_type()
You could not possibly get that as a result.
Instead, you are doing this:
model._meta.get_field('g').get_internal_type
Which, as explained here, does not call the method, it just refers to the method as a bound method object. The return value is not part of that bound method object, it's created by the method when the method is called. So, you have to call it. So you need the parentheses.
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