Python - 将行添加到正在写入的文件的顶部

Question

我正在将信息抓取到一个文本文件中，并试图将日期写在顶部。我有获取日期的方法，但不知道如何使用写入功能将其置于顶部。下面是我正在处理的内容的精简版本。

import re
import urllib2
import json
from datetime import datetime
import time

now = datetime.now()
InputDate = now.strftime("%Y-%m-%d")
Today = now.strftime("%B %d")

header = ("Today").split()

newfile = open("File.txt", "w")

### Irrelevant Info Here ###

string = title"\n"+info+"\n"
#newfile.write(header)
newfile.write(string)
print title+" written to file"

newfile.close()

Answer 1

您不能在文件开头插入内容。您需要编写一个新文件，从要插入的行开始，然后以旧文件的内容结束。与追加到末尾不同，写入文件的开头确实非常低效

这个问题的关键是使用NamedTemporaryFile .完成构建后，您可以在旧文件之上重命名它。

代码:

def insert_timestamp_in_file(filename):
    with open(filename) as src, tempfile.NamedTemporaryFile(
            'w', dir=os.path.dirname(filename), delete=False) as dst:

        # Save the new first line
        dst.write(dt.datetime.now().strftime("%Y-%m-%d\n"))

        # Copy the rest of the file
        shutil.copyfileobj(src, dst)

    # remove old version
    os.unlink(filename)

    # rename new version
    os.rename(dst.name, filename)

测试代码:

import datetime as dt
import tempfile
import shutil

insert_timestamp_in_file("file1")

文件1

I am scraping info to a text file and am trying to write the date at
the top. I have the method to grab the date but have no clue how I can
use the write function to place at top. Been trying for 2 days and all.

结果:

2018-02-15
I am scraping info to a text file and am trying to write the date at
the top. I have the method to grab the date but have no clue how I can
use the write function to place at top. Been trying for 2 days and all.