理解列表和新文件

Question

Example of two text files. The left image is before, the right one is after

我需要交换一个文件中的日期，然后使用理解列表将其放入一个新文件中。我该怎么做？这是我的：

list1 = [x.replace("\n","").replace("/"," ").split(" ") for x in open("dobA.txt")]
list2 = [(i[len(i)-2],i[len(i)-3]) for i in list1]
with open("dobB.txt", "w") as newfile:
        newfile.write()

最上面一行代码将日期变成了它们自己的字符串，例如“10”。

第二行代码交换了我需要的数字但只打印出来： [('11', '10'), ('8', '9'), ('9', '7')]

最后两个刚刚写了一个新文件

我如何交换这两个数字并将它们放在一个新文件中？谢谢。

Answer 1

首先，执行此操作：

i[-2]

而不是

i[len(i)-2]

有几个选项可以解决这个问题：

可读但不理解：

with open("old_file.txt") as old_file, open("new_file.txt", "w") as new_file:
    for line in old_file:
        name, surname, date = line.split()
        day, month, year = date.split("/")
        print(f"{name} {surname} {month}/{day}/{year}", file=new_file)

正则表达式替换：

import re
from pathlib import Path

text = Path("old_file.txt").read_text()
replaced = re.sub(r"(\d+)/(\d+)/(\d+)", r"//", text)
Path("new_file.txt").write_text(replaced)

如果你真的需要理解：

with open("old_file.txt") as old_file, open("new_file.txt", "w") as new_file:
    new_lines = [
        f"{text} {date.split('/')[1]}/{date.split('/')[0]}/{date.split('/')[2]}"
        for text, date in [line.rsplit(maxsplit=1) for line in old_file]
    ]
    print("\n".join(new_lines), file=new_file)

Answer 2

我想看看这是否可以一次性完成。它可能违背“可读性”。

翻转月份和日期的最简单方法是利用日期时间对象上的 string formatting methods。

有关格式选项，请参阅 Python strftime reference。

from pathlib import Path
import tempfile
from datetime import datetime
import operator as op

# Create temporary files for reading and writing.
_, filename = tempfile.mkstemp()
file_A = Path(filename)
_, filename = tempfile.mkstemp()
file_B = Path(filename)

contents_A = """Adam Brown 10/11/1999
Lauren Marie Smith 9/8/2001
Vincent Guth II 7/9/1980"""
file_A.write_text(contents_A)

# This version requires Python 3.8. 
# It uses the newly introduced assignment expression ":=".
# datetime objects have string formatting methods.
file_B.write_text(
    "\n".join(# re-join the lines
        [
            " ".join(# re-join the words
                (
                    # Store the split line into words. Then slice all but last.
                    " ".join((words := line.split())[:-1]),
                    # Convert the last word to desired date format.
                    datetime.strptime(words[-1], "%m/%d/%Y",).strftime("%-d/%-m/%Y",),
                )
            )
            for line in fileA.read_text().splitlines()
        ]
    )
)
print(file_B.read_text())

输出：

Adam Brown 11/10/1999

Lauren Marie Smith 8/9/2001

Vincent Guth II 9/7/1980

如果没有“:=”运算符，问题就多了一点。这意味着必须在理解中调用 line.split() 两次。

file_B.write_text("\n".join([
    " ".join(
        op.add(
            line.split()[:-1],
            [
                datetime.strptime(
                    line.split()[-1], "%m/%d/%Y",
                ).strftime("%-d/%-m/%Y",),
            ],
        )
    )
    for line in fileA.read_text().splitlines()
]))

print(file_B.read_text())

输出：

Adam Brown 11/10/1999

Lauren Marie Smith 8/9/2001

Vincent Guth II 9/7/1980

理解列表和新文件

Comprehension List and new File

python

swap

file

list