请大神看看这个代码

请教大神，以下代码为什么不能显示X轴的标签？

1. import json
   
2. import pygal
   
3. import math
   
4. 
   
5. # 将数据加载到一个列表中
   
6. filename = r'btc_close_2017.json'
   
7. with open(filename) as f:
   
8.     btc_data = json.load(f)
   
9. 
   
10. dates = []
    
11. months = []
    
12. weeks = []
    
13. weekdays = []
    
14. closes = []
    
15. 
    
16. # 遍历btc_data完成列表
    
17. for btc_dict in btc_data:
    
18.     date = btc_dict['date']
    
19.     month = int(btc_dict['month'])
    
20.     week = int(btc_dict['week'])
    
21.     weekday = btc_dict['weekday']
    
22.     close = int(float(btc_dict['close']))
    
23.     dates.append(date)
    
24.     months.append(month)
    
25.     weeks.append(week)
    
26.     weekdays.append(weekday)
    
27.     closes.append(close)
    
28. 
    
29. # 绘制图形
    
30. line_chart = pygal.Line(x_label_rotation=30, show_minor_x_labels=False)
    
31. line_chart.title = '收盘价对数变换'
    
32. line_chart.x_labels = dates
    
33. N = 20  # x轴坐标间隔20天显示一次
    
34. line_chart._x_labels_major = dates[:: N]
    
35. close_log = [math.log10(_) for _ in closes]
    
36. line_chart.add('log收盘价', close_log)
    
37. line_chart.render_to_file('收盘价折线图.svg')

复制代码

运行结果在X轴上是空白的，怎么肥四？请大神指教。