写入CSV文件的数据中的小数位数格式

Question

I have this piece of code for reading temperature from TC-08 temperaturelogger from Picotech and writing the temperature to a CSV file. The problem is that the temperatures are stored with four decimals in the file and two decimals or even one is good enough for me.

I have tried to use np.around(temp,2) and np.set_printoptions(precision=2) but none of them changes the number of decimals written to the CSV-file. Could you help me out and tell me the proper way to do it?

csv_delimiter='\t'  
file = 'test.csv'   
no_of_channels=6    #set number of channels to read
tc_type=ord('K')    #set type of element
no_of_meas = 10
time_interval= 10 #read every 10 sec

#Setup TC08
mydll = ctypes.windll.LoadLibrary('usbtc08.dll')
device = mydll.usb_tc08_open_unit()
mydll.usb_tc08_set_mains(device,50) #set the mains rejection to 50 or 60 Hz

temp = np.zeros( (9,), dtype=np.float32)
overflow_flags = np.zeros( (1,), dtype=np.int16)
mydll.usb_tc08_set_channel(device, 0, 0 )

no_of_channels +=1  #Don't want to read channel 0

for i in range(1,no_of_channels):
    mydll.usb_tc08_set_channel(device,i,tc_type)

cur_meas = 1

with open(file, 'a', newline='') as fp:
    while cur_meas <= no_of_meas:
        timeBegin = time.time()
        cur_time = datetime.datetime.strftime(datetime.datetime.now(), '%H:%M:%S') 
        a = csv.writer(fp, delimiter=csv_delimiter)
        mydll.usb_tc08_get_single(device, temp.ctypes.data, overflow_flags.ctypes.data, 0)       
        #np.around(temp,2)#I have tried this in order to get two decimals
        #np.set_printoptions(precision=2)#I have tried this in order to get two decimals
        print(temp)
        listtemp = temp[1:no_of_channels]
        print(listtemp)
        data = [[cur_time]+list(listtemp)]
        a.writerows(data)
        fp.flush() 
        os .fsync(fp.fileno())
        print(', '.join(map(str, data)))
        cur_meas += 1
        timeEnd = time.time()
        timeElapsed = timeEnd - timeBegin
        time.sleep(time_interval-timeElapsed)

mydll.usb_tc08_close_unit(device)

Answer 1

Stating the obvious, the csv is text, so the precision displayed when imported may be different for each cell. the round function does not guarantee two decimal precision, however formatting a float does.

f1 = 100.0001
f2 = 99.2345
f3 = 88.7455
f4 = 1.4589
lf1 = [f1, f2, f3, f4]

for f in lf1:
    print f
    print str(round(f, 2))
    print '{0:0.2f}'.format(f) # rounds and formats to two decimal precision

100.0001
100.0
100.00
99.2345
99.23
99.23
88.7455
88.75
88.75
1.4589
1.46
1.46