Retrieving values from mysql database and saving them to an empty array with python

Question

I have a MySQL DB (using MySQL workbench) having two tables (ecg_pat_tbl & ecg_data_tbl), and sending float values, Date and Time to columns voltage, date, and time respectively, and am also plotting a graph at the same time (voltage against time), everything is going well, now I want to retrieve both voltage and time values save them to different arrays so that I can use them for analysis, how do I go about retrieving and saving them? The code below is the function am using to plot and save to the DB.

data =[]
_condition = False
amount = 0

def graphing():
    global _condition, data
    if (_condition == True):
        try:
            identity = identity_var.get() # Getting patient ID
            date_time=datetime.datetime.now()
            my_time='{}:{}:{}'.format(date_time.hour,date_time.minute,date_time.second)
            my_date='{}/{}/{}'.format(date_time.year, date_time.month,date_time.day)
            
            serial_data = _serial.readline()
            serial_data.decode()
            
            float_data = float(serial_data[0:4])
            query = "INSERT INTO ecg_data_tbl(patient_id, voltage, date, time) VALUES(%s, %s, %s, %s)"
            mycursor.execute(query, (identity, float_data, my_date,  my_time))
            mycursor.execute("commit")
            
            data.append(float_data)
            ax.plot(data, color="blue")
            canvas.draw_idle()
    
        except ValueError as e:
            _condition = False
            start_button['state'] = NORMAL
            freeze_button['state'] = DISABLED
            save_button['state'] = DISABLED
            insert_button['state'] = DISABLED
            messagebox.showinfo("Connection", "Check connnection of the patient cable")

all responses are appreciated.

tarro · Accepted Answer · 2021-10-28 20:01:49Z

1

Correct me if I'm wrong, but it seems your only issue is unzipping the values from the format cursor's return value: (time_0, volt_0), (time_1, volt_1), .... The code should look something like this.


query = "SELECT time, voltage FROM ecg_data_tbl WHERE patient_id=?"
result = cursor.execute(query, (identity,)).fetchall()
# (time_0, volt_0), (time_1, volt_1), ...
times, volts = list(zip(*result))
# (time_0, time_1, ...), (volt_0, volt_1, ...)

answered Oct 28, 2021 at 20:01

tarro

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