human
Here's a good function header given the following:
I wrote the below code

    def rename_field(key, data, errors, context):
        index = max(([int(k[1]) for k in data.keys() if ((len(k) == 3) and (k[0] == new))] + [(-1)]))
        for field_name in data.keys():
            if ((field_name[0] == old) and data.get(field_name)):
                new_field_name = list(field_name)
                new_field_name[0] = new
                if (len(new_field_name) > 1):
                    new_field_name[1] = ((int(new_field_name[1]) + index) + 1)
                data[tuple(new_field_name)] = data[field_name]
                data.pop(field_name)
    return rename_field

What's a good function header?
assistant
#Here's a good function header.

def rename(old, new):