全部代码如下：
import json
import pygal
import math
from itertools import groupby
filename = 'btc_close_2017.json'
with open(filename) as f:
btc_data = json.load(f)
dates = []
months = []
weeks = []
weekdays = []
closes = []
for btc_dict in btc_data:
dates.append(btc_dict['date'])
months.append(int(btc_dict['month']))
weeks.append(int(btc_dict['week']))
weekdays.append(btc_dict['weekday'])
closes.append(int(float(btc_dict['close'])))
line_chart = pygal.Line(x_label_rotation=20, show_minor_x_labels=False)
line_chart.title = '收盘价（￥）'
line_chart.x_labels = dates
N = 20
line_chart.x_labels_major = dates[::N]
def draw_line(x_data, y_data, title, y_legend):
xy_map = []
for x, y in groupby(sorted(zip(x_data, y_data)), key=lambda _: _[0]):
y_list = [v for _, v in y]
xy_map.append([x, sum(y_list) / len(y_list)])
x_unique, y_mean = [*zip(*xy_map)]
line_chart = pygal.Line()
line_chart.title = title
line_chart.x_labels = x_unique
line_chart.add(y_legend, y_mean)
line_chart.render_to_file(title + '.svg')
return line_chart
idx_month = dates.index('2017-12-01')
line_chart_month = draw_line(months[:idx_month], closes[:idx_month],'收盘价月日均值（￥）', '月日均值')
line_chart_month
运行的时候，错误提示：object of type 'int' has no len()，代码里面只有
xy_map.append([x, sum(y_list) / len(y_list)])
这行出现了len函数，我理解对象y list应该是一个列表啊，这段已经是我从书上摘抄下来的原文，不知道是错在哪里了? 麻烦路过的大神们帮忙看看！
