在 Python 中删除文件行

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，他们会更新到新的高分，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()

有谁知道如何在文件中用新的替换旧的？

Answer 1

简单的答案是：不可能。操作系统及其文件操作没有“行”的概念。它们处理二进制数据块。一些库（例如 Python 的标准库）在此之上为 阅读 行提供了方便的抽象 - 但它们不允许您处理单个行。

那么如何解决这个问题呢？只需打开文件，读取所有行，在适当的位置操作有问题的行，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 2

我建议您改用某种标准格式来保存信息，例如 JSON、YAML、XML、CSV、pickle 或其他。然后你需要将文件读取并解析为原生数据结构（在这种情况下可能是dict），修改它（这很简单），然后写回来。

以json 为例（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)

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

Answer 3

先，后

b = a.read()

写

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

看看会带你去哪里。