Python Matplotlib多数据集折线图共用Y轴显示异常问题

我是Python新手，第一次用Matplotlib库。尝试在单张折线图中绘制多组数据集，但Y轴无法正常显示。X轴为秒级时间数据，Y轴为数值型数据，所有数据以字典键值对形式存储，值为列表。单独绘制一组数据时显示正常（Plot 1），但添加多组数据后，Y轴似乎为每组数据显示独立的数值范围（Plot 2）。我知道通常会使用numpy数组而非列表，但当前需沿用现有数据格式。此前查过类似问题案例，但遇到的情况与我不同。

代码如下：

import matplotlib.pyplot as plt

kline_data_dict = {'time': ['14:27:00', '14:27:00', '14:27:00', '14:27:00', '14:27:02', '14:27:02', '14:27:02', '14:27:02', '14:27:04', '14:27:04'], 'open': ['20854.76000000', '20854.76000000', '20854.76000000', '20854.76000000', '20861.38000000', '20861.38000000', '20861.38000000', '20861.38000000', '20861.38000000', '20861.38000000'], 'close': ['20862.47000000', '20862.47000000', '20862.47000000', '20862.47000000', '20861.80000000', '20861.80000000', '20861.80000000', '20861.80000000', '20864.65000000', '20864.65000000'], 'high': ['20879.99000000', '20879.99000000', '20879.99000000', '20879.99000000', '20864.16000000', '20864.16000000', '20864.16000000', '20864.16000000', '20869.73000000', '20869.73000000'], 'low': ['20846.30000000', '20846.30000000', '20846.30000000', '20846.30000000', '20860.27000000', '20860.27000000', '20860.27000000', '20860.27000000', '20860.27000000', '20860.27000000']}

plt.plot(kline_data_dict['time'], kline_data_dict['low'])
plt.plot(kline_data_dict['time'], kline_data_dict['high'])
plt.show()

问题核心是Y轴数据为字符串类型，而非数值类型。Matplotlib处理字符串数据时会将其视为离散分类值，而非连续数值，导致多组数据叠加时出现独立的Y轴范围。

无需转换为numpy数组，直接将字典中数值类的字符串转为浮点数即可，保留原数据格式的处理代码如下：

import matplotlib.pyplot as plt

kline_data_dict = {'time': ['14:27:00', '14:27:00', '14:27:00', '14:27:00', '14:27:02', '14:27:02', '14:27:02', '14:27:02', '14:27:04', '14:27:04'], 'open': ['20854.76000000', '20854.76000000', '20854.76000000', '20854.76000000', '20861.38000000', '20861.38000000', '20861.38000000', '20861.38000000', '20861.38000000', '20861.38000000'], 'close': ['20862.47000000', '20862.47000000', '20862.47000000', '20862.47000000', '20861.80000000', '20861.80000000', '20861.80000000', '20861.80000000', '20864.65000000', '20864.65000000'], 'high': ['20879.99000000', '20879.99000000', '20879.99000000', '20879.99000000', '20864.16000000', '20864.16000000', '20864.16000000', '20864.16000000', '20869.73000000', '20869.73000000'], 'low': ['20846.30000000', '20846.30000000', '20846.30000000', '20846.30000000', '20860.27000000', '20860.27000000', '20860.27000000', '20860.27000000', '20860.27000000', '20860.27000000']}

# 将数值型字符串批量转为浮点数
for key in ['open', 'close', 'high', 'low']:
    kline_data_dict[key] = [float(val) for val in kline_data_dict[key]]

plt.plot(kline_data_dict['time'], kline_data_dict['low'], label='Low')
plt.plot(kline_data_dict['time'], kline_data_dict['high'], label='High')
plt.xlabel('时间')
plt.ylabel('价格')
plt.legend()
plt.show()

处理后Y轴会显示统一的连续数值范围，多组折线图可正常叠加显示。

内容的提问来源于stack exchange，提问作者formerlolz