使用Python删除文件中的特定行

Question

假设我有一个充满昵称的文本文件.如何使用Python从此文件中删除特定昵称？

Answer 1

假设您的文件的格式为每行一个昵称,请使用此方法.

首先,打开文件:

with open("yourfile.txt", "r") as f:
    lines = f.readlines()
with open("yourfile.txt", "w") as f:
    for line in lines:
        if line.strip("\n") != "nickname_to_delete":
            f.write(line)

接下来,从文件中获取所有行:

with open("yourfile.txt", "r") as f:
    lines = f.readlines()
with open("yourfile.txt", "w") as f:
    for line in lines:
        if line.strip("\n") != "nickname_to_delete":
            f.write(line)

现在您可以关闭文件:

with open("yourfile.txt", "r") as f:
    lines = f.readlines()
with open("yourfile.txt", "w") as f:
    for line in lines:
        if line.strip("\n") != "nickname_to_delete":
            f.write(line)

并在写入模式下重新打开它:

with open("yourfile.txt", "r") as f:
    lines = f.readlines()
with open("yourfile.txt", "w") as f:
    for line in lines:
        if line.strip("\n") != "nickname_to_delete":
            f.write(line)

然后,写回您的行,但要删除的行除外.您可能希望将更strip("\n")改为结束文件使用的任何行.

with open("yourfile.txt", "r") as f:
    lines = f.readlines()
with open("yourfile.txt", "w") as f:
    for line in lines:
        if line.strip("\n") != "nickname_to_delete":
            f.write(line)

最后,再次关闭文件.

with open("yourfile.txt", "r") as f:
    lines = f.readlines()
with open("yourfile.txt", "w") as f:
    for line in lines:
        if line.strip("\n") != "nickname_to_delete":
            f.write(line)

Answer 2

只需一次打开即可解决此问题:

with open("target.txt", "r+") as f:
    d = f.readlines()
    f.seek(0)
    for i in d:
        if i != "line you want to remove...":
            f.write(i)
    f.truncate()

此解决方案以r/w模式("r +")打开文件,并使用seek重置f指针,然后截断以删除最后一次写入后的所有内容.

Answer 3

最好和最快的选择,而不是将所有内容存储在列表中并重新打开文件来编写它,我认为在其他地方重写文件.

with open("yourfile.txt", "r") as input:
    with open("newfile.txt", "w") as output: 
        for line in input:
            if line.strip("\n") != "nickname_to_delete":
                output.write(line)

而已!在一个循环和一个循环只有你可以做同样的事情.它会快得多.

Answer 4

这是来自@Lother答案的"分叉" (我认为这应该被认为是正确的答案).

对于这样的文件:

$ cat file.txt 
1: october rust
2: november rain
3: december snow

来自Lother的解决方案的这个分支工作正常:

#!/usr/bin/python3.4

with open("file.txt","r+") as f:
    new_f = f.readlines()
    f.seek(0)
    for line in new_f:
        if "snow" not in line:
            f.write(line)
    f.truncate()

改进:

• with open,放弃使用 f.close()
• 更清楚地if/else评估当前行中是否存在字符串

Answer 5

在第一遍中读取行并在第二遍中进行更改（删除特定行）的问题在于，如果文件大小很大，则会耗尽 RAM。相反，更好的方法是逐行读取行，然后将它们写入单独的文件中，删除不需要的行。我已经对 12-50 GB 的文件运行了这种方法，并且 RAM 使用率几乎保持不变。只有 CPU 周期显示正在进行的处理。

Answer 6

尚未提出一个简单的解决方案：

with open( file_of_nicknames, "r+" ) as f:
    lines = f.readlines()           # Get a list of all lines
    f.seek(0)                       # Reset the file to the beginning

    idx = lines.index("Nickname\n") # Don't forget the '\n'
    lines.pop( idx )                # Remove the corresponding index

    f.truncate()                    # Stop processing now
                                    # because len(file_lines) > len( lines ) 
    f.writelines( lines )           # write back

受到先例答案的启发