python csv，只写一次标题
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python csv, writing headers only once
提问by cyberbemon
So I have a program that creates CSV from .Json.
所以我有一个从 .Json 创建 CSV 的程序。
First I load the json file.
首先我加载json文件。
f = open('Data.json')
data = json.load(f)
f.close()
Then I go through it, looking for a specific keyword, if I find that keyword. I'll write everything related to that in a .csv file.
然后我通过它，寻找一个特定的关键字，如果我找到了那个关键字。我将在 .csv 文件中写下与此相关的所有内容。
for item in data:
if "light" in item:
write_light_csv('light.csv', item)
This is my write_light_csvfunction :
这是我的write_light_csv功能：
def write_light_csv(filename,dic):
with open (filename,'a') as csvfile:
headers = ['TimeStamp', 'light','Proximity']
writer = csv.DictWriter(csvfile, delimiter=',', lineterminator='\n',fieldnames=headers)
writer.writeheader()
writer.writerow({'TimeStamp': dic['ts'], 'light' : dic['light'],'Proximity' : dic['prox']})
I initially had wb+as the mode, but that cleared everything each time the file was opened for writing. I replaced that with aand now every time it writes, it adds a header. How do I make sure that header is only written once?.
我最初是wb+作为模式，但是每次打开文件进行写入时都会清除所有内容。我用它替换了它，a现在每次写入时，它都会添加一个标题。如何确保标题只写入一次？。
采纳答案by Igor Hatarist
You could check if file is already exists and then don't call writeheader()since you're opening the file with an append option.
您可以检查文件是否已经存在，然后不要调用，writeheader()因为您正在使用附加选项打开文件。
Something like that:
类似的东西：
import os.path
file_exists = os.path.isfile(filename)
with open (filename, 'a') as csvfile:
headers = ['TimeStamp', 'light', 'Proximity']
writer = csv.DictWriter(csvfile, delimiter=',', lineterminator='\n',fieldnames=headers)
if not file_exists:
writer.writeheader() # file doesn't exist yet, write a header
writer.writerow({'TimeStamp': dic['ts'], 'light': dic['light'], 'Proximity': dic['prox']})
回答by eumiro
Can you change the structure of your code and export the whole file at once?
您可以更改代码结构并立即导出整个文件吗？
def write_light_csv(filename, data):
with open (filename, 'w') as csvfile:
headers = ['TimeStamp', 'light','Proximity']
writer = csv.DictWriter(csvfile, delimiter=',', lineterminator='\n',fieldnames=headers)
writer.writeheader()
for item in data:
if "light" in item:
writer.writerow({'TimeStamp': item['ts'], 'light' : item['light'],'Proximity' : item['prox']})
write_light_csv('light.csv', data)
回答by SIslam
I would use some flagand run a check before writing headers! e.g.
flag在写之前我会使用一些并进行检查headers！例如
flag=0
def get_data(lst):
for i in lst:#say list of url
global flag
respons = requests.get(i)
respons= respons.content.encode('utf-8')
respons=respons.replace('\','')
print respons
data = json.loads(respons)
fl = codecs.open(r"C:\Users\TEST\Desktop\data1.txt",'ab',encoding='utf-8')
writer = csv.DictWriter(fl,data.keys())
if flag==0:
writer.writeheader()
writer.writerow(data)
flag+=1
print "You have written % times"%(str(flag))
fl.close()
get_data(urls)
回答by Gilbert
You can check if the file is empty
您可以检查文件是否为空
import csv
import os
headers = ['head1', 'head2']
for row in interator:
with open('file.csv', 'a') as f:
file_is_empty = os.stat('file.csv').st_size == 0
writer = csv.writer(f, lineterminator='\n')
if file_is_empty:
writer.writerow(headers)
writer.writerow(row)
回答by DeveScie
Just another way:
只是另一种方式：
with open(file_path, 'a') as file:
w = csv.DictWriter(file, my_dict.keys())
if file.tell() == 0:
w.writeheader()
w.writerow(my_dict)
回答by rearThing
You can use the csv.SnifferClass and
您可以使用csv.Sniffer类和
with open('my.csv', newline='') as csvfile:
if csv.Sniffer().has_header(csvfile.read(1024))
# skip writing headers
