使用 python 将文本文件中的一行替换为任何新行

Question

假设我有一个文本文件 details.txt
details.txt

id=0=pending
id=1=pending
id=abc2=pending
id=x2=found
#cursor always points to the new line since I am appending \n in the end of each line

现在我有一个 python 文件说 update.py ，我想做的是替换具有特定 ID 的行待定（例如：id=1=pending）与 (id=1=missing) 或 (id=1=found).

PS。请注意，我们只是将 pending 更改为 missing 或 found ，其余 id=1= 相同。例如，如果我们将 details.txt 中的 id=1=pending 替换为 id=1=found，它应该如下所示：

id=0=pending
id=1=found
id=abc2=pending
id=x2=found
#cursor always points to the new line since I am appending \n in the end of each line

这是我写的
update.py

f = open("details.txt","r+")
temp = f.readlines()
for line in temp:
    word = line.split('=')#using = as a delimiter
    if word[1]=="1" and word[2]=="pending\n":    #pending\n because while writing, we are appending \n to each line
        striped = line.strip()
        new_line = striped.replace("pending","found")
        new_content = new_line     #id=1=found
        pos = f.tell()      #it will give the current position
        if pos-len(line)-1>=0:    #checking whether we have any line or not
            pos = pos-len(line)-1     #going to the start of a line and -1 to remove \n
        f.seek(pos)        #setting the pointer to the start of the line we want to replace , (start of 2nd line in this case)
        f.write(new_content)         #writing the content

f.close()

我得到的输出

id=0=pending
id=1=foundng
id=abc2=pending
id=x2=found
#cursor always points to the new line since I am appending \n in the end of each line

所以我们得到的不是 (id=1=found) (id=1=foundng) ，因为 len(found ) 是 5 并且 len(pending) 是 7 ，所以在 pending 结束时额外的 2 个字符即 ng 不会被替换。

请告诉我该怎么做。
另外请告诉我，如果我想删除特定行，那么我该怎么做。
例如：
如果我想删除行 (id=abc2=pending) ，我应该怎么做。
输出应该是这样的：

id=0=pending
id=1=pending
id=x2=found
#cursor always points to the new line since I am appending \n in the end of each line

请注意，该行与\n

一起被删除任何帮助将不胜感激

Answer 1

不用 if 语句，使用正则表达式会有所帮助，

由于您要查找后跟单词 'pending' 的特定 ID，因此一个简单的正则表达式："id=your_id=pending" 将起作用。

然后您可以使用re.sub将整行替换为您想要的内容。这里id=your_id=missing/found"

Note : this answer is probably not the best one, since you re-write most of the lines, but for small files, works perfectly.

import re

FILENAME = "textfile.txt"

def update_file(filename,id,word_to_add,lines_to_remove):
    
    lines_to_remove = [s + "\n" for s in lines_to_remove] 
    #adding \n to all lines you want to remove

    pattern =re.compile("^id="+str(id)+"=pending")
    new_lines=[]

    with open(FILENAME,'r+') as  file:

            for line in file:
                if line not in lines_to_remove: # keeping only lines desired

                    new_lines.append(pattern.sub("id=1="+word_to_add,line))

    with open(FILENAME,'w') as  file:
        file.writelines(new_lines)
    
    return 0


update_file(FILENAME,1,"missing",["id=abc2=pending"])

#Output
#id=0=pending
#id=1=missing

Answer 2

如果您打印 new_content 而不是 f.write(new-content)。可以看出问题实际上不在替换函数中，单词被替换为它应该

        # f.write(new_content)
        print(new_content)

输出：id=1=found 应该是

问题是，当你覆盖之前存在的文件时，它会替换文件中已经存在的字符，在这种情况下，碰巧“pending”的最后两个字母不需要将被覆盖。

要解决这个问题，您必须重写整个文件：

f = open("details.txt","r")
temp = f.readlines()

output_text = []
for line in temp:
    word = line.split('=')
    if word[1]=="1" and word[2]=="pending\n":
        line = line.replace("pending\n", "found\n") # replace pending with found 
    output_text.append(line)
f.close()

f = open("details.txt", "w")
f.write("".join(output_text))
f.close()

现在文件是：

id=0=pending
id=1=found
id=abc2=pending
id=x2=found

使用 python 将文本文件中的一行替换为任何新行

Replace a line in a text file with any new line using python

python

file-handling