python画折线图

一、从mysql库中查询数据

新建一个py文件，写查询数据的方法

import pymysql

def Read_database (sql):
    user_name='root'
    password='root'
    address='localhost'
    port='3306'
    database_name='test'

    conn = pymysql.connect(host = address,user = user_name,passwd = password,\
                           db = database_name , port = int(port) ,charset = "utf8mb4")
    try:
        #df = pd.read_sql (sql,con = conn)
        cursor = conn.cursor()
        cursor.execute(sql)
        df = cursor.fetchall()
    except:
        print ('\n Reading Error  \n')    
    finally:
        conn.close()
    print ('\n Completion of data reading \n')    
    return (df) 

二、再新建py文件，查询出数据并构建折线图的数据

indexData = Read_database("SELECT * FROM `cryindex` where CreateTime >='2019-01-01' and CreateTime < '2020-10-17' ORDER BY CreateTime")

indexList = []
timeList = []

for i in indexData:
    indexList.append(i[1])
    timeList.append(i[0])

三、画出折线图

# plot中参数的含义分别是横轴值，纵轴值，线的形状，颜色，透明度,线的宽度和标签
plt.plot(timeList,
         indexList,
         'ro-',
         color='#4169E1',
         alpha=0.8,
         linewidth=1,
         label='I')

# 显示标签，如果不加这句，即使在plot中加了label='一些数字'的参数，最终还是不会显示标签
plt.legend(loc="upper right")
plt.xlabel('x轴数字')
plt.ylabel('y轴数字')

plt.show()