删除 Python 中的文件行

Question

我正在尝试创建一个接受用户名和高分的程序，如果他们已经是用户，他们会更新到他们的新高分，或者如果不是，则只添加高分。

我的代码是：

try:
    a = open("data", "r+")
except FileNotFoundError:
    a = open("data", "w")
a = open("data", "r+")
b = a.read()
user = input("Username: ")
user2 = list(user)
if user in b:
    old = input("What is your old highscore? ")
    new = input("What is your new highscore? ")
    b2 = b.split()
    for line in b2:
        #Where I want to edit.
        line=line.replace(old, new)
        print(line)

else:
    new = input("What is your highscore? ")
    a.write(user + " " + new + "\n")
a.close()

有谁知道如何将文件中的旧文件替换为新文件？

Answer 1

先关，后

b = a.read()

写

a.close()
a = open("data","w")

看看它会带你去哪里。

Answer 2

简单的回答是：这是不可能的。操作系统及其文件操作没有 "lines" 的概念。它们处理二进制数据块。一些库，例如 Python 的标准库，在上面为 reading 行提供了一个方便的抽象 - 但它们不允许您处理单独的行。

那么如何解决问题呢？只需打开文件，读取所有行，就地处理有问题的行，然后再次写出整个文件。

 import tempfile

 highscore_file = tempfile.mktemp()

 with open(highscore_file, "w") as outf:
     outf.write("peter 1000\nsarah 500\n")

 player = "sarah"
 score = 2000

 output_lines = []
 with open(highscore_file) as inf:
     for line in inf:
         if player in line:
             # replace old with new line. Don't forget trailing newline!
             line = "%s %i\n" % (player, score)
         output_lines.append(line)

 with open(highscore_file, "w") as outf:
     outf.write("".join(output_lines))



 with open(highscore_file) as inf:
     print inf.read()

Answer 3

我建议您改用一些标准格式来保存信息，例如 JSON、YAML、XML、CSV、pickle 或其他格式。然后你需要的是读取文件并将其解析为本机数据结构（在这种情况下可能是dict），修改它（这是微不足道的），然后将其写回。

带有 json 的示例（人类可读，非常易于使用）：

import json

# loading data
try:
    with open("data") as a:
        b = json.load(a) # b is dict
except FileNotFoundError:
    b = {}

# user 
name = input("What's your name? ")
score = int(input("What's your high score? "))

# manipulating data
b[name] = score

# writing back 
with open("data", "w") as a:
    json.dump(b, a)

带有 shelve 的示例（不是人类可读的，但非常易于使用）：

import shelve

name = input("What's your name? ")
score = int(input("What's your high score? "))

with shelve.open("bin-data") as b:
    b[name] = score # b is dict-like

删除 Python 中的文件行

Deleting File Lines in Python

python

file

python-3.5