为什么世界地图不显示数据？

Question

我写了这个Python程序，但是我不确定为什么它只出现一个没有数据的空映射。我在代码中做错了什么吗？

代码如下：

import csv

from pygal.maps.world import World

from pygal.style import LightColorizedStyle as LCS, RotateStyle as RS

from country_codes import get_country_code

#load the data into a list.
filename = 'expense.csv'
with open(filename) as f:
    reader = csv.reader(f)
    header_row = next(reader)
    header_row = next(reader)
    header_row = next(reader)
    header_row = next(reader)
    header_row = next(reader)

    cc_expenses = {}

    country_name, expense = [], []
    for row in reader:
        country_name.append(row[0])
        expense.append(row[61])
        code = get_country_code(country_name)
        if code:
            cc_expenses[code] = expense

wm_style = RS('#336699', base_style=LCS)            

wm = World(style=wm_style)
wm.title = 'World Expense(% of GDP) in 2017, by Country'
wm.add(code, expense)

wm.render_to_file('world_expenses.svg')

请帮助！非常感谢你！