ValueError: no enough values to unpack (expected 2, got 0) Python and tkinter and Mysql

Posted 2023-03-23

【中文标题】ValueError: no enough values to unpack (expected 2, got 0) Python and tkinter and Mysql

【英文标题】：ValueError: not enough values to unpack (expected 2, got 0) Python and tkinter and Mysql

【发布时间】：2021-12-31 01:35:12

【问题描述】：

我需要帮助。我有一个patient_results_tbl，如下所示，我想根据patient_id 和date 检索voltage 和time，非常多。

# patient_id,    voltage,     time,          date
'260939631',     '329',       '18:34:37',    '2021-11-05'
'260939631',     '334',       '18:34:39',    '2021-11-05'
'260939631',     '352',       '18:34:39',    '2021-11-05'
'260939631',     '341',       '18:51:01',    '2021-11-13'
'260939631',     '338',       '18:51:02',    '2021-11-13'
'260939631',     '331',       '18:51:03',    '2021-11-13'
'260939631',     '324',       '18:51:04',    '2021-11-13'
'260939631',     '319',       '18:51:05',    '2021-11-13'
'785393661',     '274',       '18:58:07',    '2021-11-13'
'785393661',     '280',       '18:58:08',    '2021-11-13'
'785393661',     '285',       '18:58:08',    '2021-11-13'
'785393661',     '290',       '18:58:09',    '2021-11-13'

我使用的代码如下：

def analyze_voltage_time():
            start_point = int(start_point_entry.get()) # getting from entry box
            end_point = int(end_point_entry.get())  # getting from entry box
            step = int(step_point_entry.get())  # getting from entry box
            start = get_date2()  # getting from tkcalender date picker
            _id = id_selector.get() # # getting from combobox
            pat_id = _id[:9]
            #query = "SELECT voltage, time FROM patient_results_tbl where patient_id =  " +pat_id
            #mycursor.execute(query, )
            query = "SELECT voltage, time FROM patient_results_tbl WHERE 'date' =%s AND 'patient_id' =%s"
            mycursor.execute(query, (start, pat_id))
            result = mycursor .fetchall()
            print(result)  # For checking 
            print(start)     # For checking purpose 
            print(pat_id)   # For checking purpose
            voltage, time = list(zip(*result))  # ValueError: not enough values to unpack (expected 2, got 0)
            for volts in voltage:
                voltage_container.append(volts)
            for tim in time:
                time_container.append(str(tim))
            try:
                user_data = range(start_point, end_point, step)
                for i in user_data:
                    plt_voltage.append(voltage_container[i])
                    plt_time.append(time_container[i])
    
            except ValueError:
                user_data = range(start_point, end_point)
                for i in user_data:
                    plt_voltage.append(voltage_container[i])
                    plt_time.append(time_container[i])
                
            my_ax1.plot(plt_time, plt_voltage, color="red")        
            my_canvas1.draw_idle()
            analyse_btn['state'] = DISABLED

将上述代码作为独立应用运行时会出现以下错误：

[]
05/11/2021
260939631
Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\Kennedy Mulenga\AppData\Local\Programs\Python\Python39\lib\tkinter\__init__.py", line 1892, in __call__
    return self.func(*args)
  File "C:\Users\Kennedy Mulenga\Desktop\Level 5\18136709_BIT_280_Arduino_ECG_Project\18136709\18136709_ECG_LArdmon_APP_Final.py", line 418, in <lambda>
    analyse_btn = Button( tools_frame, text='Analyse', width = 8, height = 2, command = lambda :[get_date2(), analyze_voltage_time()])
  File "C:\Users\Kennedy Mulenga\Desktop\Level 5\18136709_BIT_280_Arduino_ECG_Project\18136709\18136709_ECG_LArdmon_APP_Final.py", line 285, in analyze_voltage_time
    voltage, time = list(zip(*result))
ValueError: not enough values to unpack (expected 2, got 0)

如果我使用已注释掉的查询运行，它会返回与 patient_id 相关的所有记录，这没问题。 并且还直接在mysql 工作台中运行查询SELECT voltage, time FROM patient_results_tbl WHERE date = 13/11/2021 AND patient_id = 785393661 返回0 rows，但如果我用OR 替换AND 我会得到一些结果

# patient_id    voltage    time       date
785393661       274        18:58:07   2021-11-13
785393661       280        18:58:08   2021-11-13
785393661       285        18:58:08   2021-11-13
785393661       290        18:58:09   2021-11-13

不知道哪里做得不好，或者有什么办法？

【参考方案1】：

您应该以minimal, reproducible example 的形式提供您的代码，如果我们可以复制粘贴并立即得到相同的错误，则更容易尝试和修复。

您在查询中输入的日期格式为“dd/mm/yyyy”，但您的表格的格式为“yyyy-mm-dd”。因此，您的结果最终成为一个空列表，您可以看到它打印在您的回溯上方，这给了您ValueError。

【讨论】：

当插入格式接受的数据库时，但我已将其更改为适合数据库显示的内容，并且我找到了一种可行的方法。

@Kennerdol 道歉，没有实际数据库很难找到问题

【参考方案2】：

我已经换了行：

query = "SELECT voltage, time FROM patient_results_tbl WHERE 'date' =%s AND 'patient_id' =%s"
            mycursor.execute(query, (start, pat_id))

与：

mycursor.execute("SELECT voltage, time FROM patient_results_tbl WHERE date =%s AND patient_id =%s", (start, pat_id))

通过删除 date 和 pat_id 周围的引号 现在已经奏效了，如果有更好的方法，我将不胜感激并感谢。