python中的csv标头仅在第一行？

Question

我编写了一个 python 程序，它每分钟对网络服务器进行一次 api 调用，然后解析 json 响应并将解析后的值保存到 csv 文件中。

这是将值保存到 csv 文件中的代码：

with open('data.csv', 'a', newline='') as file:
    writer = csv.writer(file)
    writer.writerow([current_time,SHORTPERC, LONGPERC, SHORTvolume, longVolume, longPositions, shortPositions])

我怎样才能让它只在最上面一行而不是每一行保存一次标题？

更新：

这里有更多代码来调用 api 并将数据写入文件：

from apscheduler.schedulers.blocking import BlockingScheduler
from apscheduler.triggers.cron import CronTrigger
import requests
import json
import csv
from datetime import datetime






def fn():
    print("Starting...")
    session_id = "auZsJ4F2RsQNJxSPTMDt2238324"
    Outlook='http://www.myfxbook.com/api/get-community-outlook.json?session=' + session_id
    Outlook_response = requests.get(Outlook)
    Outlook_data = Outlook_response.json()['symbols']
    now = datetime.now()
    current_time = now.strftime("%H:%M")





    EURUSD=Outlook_data[0]
    SHORTPERC=EURUSD['shortPercentage']
    LONGPERC =EURUSD['longPercentage']
    SHORTvolume=EURUSD['shortVolume']
    longVolume=EURUSD['longVolume']
    longPositions=EURUSD['longPositions']
    shortPositions=EURUSD['shortPositions']
    with open('data.csv', 'a', newline='') as file:
        writer = csv.writer(file)
        writer.writerow([current_time,SHORTPERC, LONGPERC, SHORTvolume, longVolume, longPositions, shortPositions])
    with open('data1.csv', 'a', newline='') as file:
        writer = csv.writer(file)
        writer.writerow([SHORTvolume, longVolume])
    with open('data2.csv', 'a', newline='') as file:
        writer = csv.writer(file)
        writer.writerow([SHORTPERC, LONGPERC])

我不能发布完整的代码，因为它有大约 700 行长，会非常难看，但是上面提到的代码应该可以创建 csv 文件

这是我的一个 csv 文件的外观：

07:11,31,69,555.55,1265.14,4750,2607
07:12,31,69,555.55,1265.16,4751,2607
07:13,31,69,555.55,1265.16,4751,2607
07:14,30,70,555.56,1267.36,4752,2608
07:15,30,70,555.56,1267.36,4752,2608
07:16,30,70,555.56,1267.36,4752,2608
07:17,30,70,555.46,1267.36,4752,2607
07:18,31,69,558.61,1267.36,4752,2610
07:19,31,69,558.61,1267.37,4753,2610
07:20,31,69,561.58,1267.37,4753,2611
07:21,31,69,561.61,1267.37,4753,2613
07:22,31,69,561.65,1267.37,4753,2614
07:23,31,69,561.65,1267.36,4752,2614

这只是 csv 文件的一部分，随着时间的推移，更多的行会不断增加

编辑 2： Sparkofska 建议的答案似乎有效，但不知何故，它最终在每一行之间给出了一个空行，如下所示：

时间,ShortPer,LongPer,ShortVolume,LongVolume,ShortPosition,LongPosition

05:47,44,56,19528.8,24789.27,65223,48630

05:48,44,56,19529.04,24789.27,65223,48633

代码：

EURUSD=Outlook_data[0]
SHORTPERC=EURUSD['shortPercentage']
LONGPERC =EURUSD['longPercentage']
SHORTvolume=EURUSD['shortVolume']
longVolume=EURUSD['longVolume']
longPositions=EURUSD['longPositions']
shortPositions=EURUSD['shortPositions']
filename='EURUSD.csv';

def write_row_header_aware(filename, row):

     
    if not os.path.exists(filename) or os.stat(filename).st_size == 0:
         
        with open(filename, 'a') as file:
            writer = csv.writer(file)
            writer.writerow(['Time', 'ShortPer', 'LongPer','ShortVolume','LongVolume','ShortPosition','LongPosition'])

     
    with open(filename, 'a') as file:
        writer = csv.writer(file)
        writer.writerow([current_time,SHORTPERC, LONGPERC, SHORTvolume, longVolume, longPositions, shortPositions])
    
write_row_header_aware(filename, [current_time,SHORTPERC, LONGPERC, SHORTvolume, longVolume, longPositions, shortPositions])
print("done...")

Answer 1

请检查文件是否存在，如果已经存在，请使用追加将行写入文件，否则写入标题。通过这种方式，您可以避免多次写入标题。请refer to this link

Answer 2

您可以包装writerow 函数，让它在需要时自动添加标题。

如果您的输出 csv 文件不为空，我们可以断言标题已写入并简单地附加该行。否则（文件不存在或为空）我们在追加行之前写入标题。

import os

def write_row_header_aware(filename, row):

    # in case file doesn't exist or is empty
    if not os.path.exists(filename) or os.stat(filename).st_size == 0:
        # write header
        with open(filename, 'a', newline='') as file:
            writer = csv.writer(file)
            writer.writerow(['current_time', 'SHORTPERC', 'LONGPERC', ...])

    # write line as usual
    with open(filename, 'a', newline='') as file:
        writer = csv.writer(file)
        writer.writerow(row)
    
write_row_header_aware('data.csv', [current_time, SHORTPERC, LONGPERC, ...])