Python 从文件中删除一行

Question

我正在努力弄清楚应该如何从文件中删除一行。下面是代码

#!/usr/bin/python
import argparse
import re
import string

##getting user inputs
p = argparse.ArgumentParser()
p.add_argument("input", help="input the data in format ip:port:name", nargs='*')  
args = p.parse_args()
kkk_list = args.input


def printInFormat(ip, port, name):
    formattedText = '''HOST Address:{ip}:PORT:{port} 
                        mode tcp 
                        bind {ip}:{port} name {name}'''.format(ip=ip, 
                                                                port=port, 
                                                                name=name)
    textWithoutExtraWhitespaces =  '\n'.join([line.strip() for line in formattedText.splitlines()])
    # you can break above thing
    # text = ""
    # for line in formattedText.splitlines():
    #       text += line.strip()
    #       text += "\n" 

    return(formattedText)

#####here im writing writing the user inoput to a file and it works great.
#with open("file.txt", "a") as myfile:
#    for kkk in kkk_list:
#         ip, port, name = re.split(":|,", kkk)
#         myfile.write(printInFormat(ip, port, name))

###### here is where im struggling. 
for kkk in kkk_list:
    ip, port, name = re.split(":|,", kkk)
    tobedel = printInFormat(ip, port, name)  
    f = open("file.txt", "r+")
    d = f.readlines()
    f.seek(0)
    if kkk != "tobedel":
        f.write(YY)
f.truncate()
f.close()

如您所见，我在 file.txt 后面附加了用户输入。即（格式：IP：端口：名称）。当脚本执行为 ./script.py 192.168.0.10:80:string 192.168.0.10:80:string

时，文件将包含以下条目

Host Address:192.168.0.10:PORT:80
mode tcp
bind 192.168.0.10:80 abc    
Host Address:10.1.1.10:PORT:443
mode tcp
bind 10.1.1.10:443 xyz

现在，当用户以相同方式输入时，我想删除 file.txt 中的行。上面的代码是运行没有任何反应。我是初学者，如果您能帮助我理解，我将不胜感激。此问题与

有关

Answer 1

有多种方法可以做到。我试图创建一个新文件，保留所有块。您可以删除旧文件并将新文件重命名为旧文件。以下是相同的工作代码。

 #!/usr/bin/python
 import argparse
 import re
 import string

##getting user inputs
p = argparse.ArgumentParser()
p.add_argument("input", help="input the data in format ip:port:name", nargs='*')  
args = p.parse_args()
kkk_list = args.input # ['192.168.1.10:80:name1', '172.25.16.2:100:name3']



# returns the next block from the available file. Every block contains 3 lines as per definition.
def getNextBlock(lines, blockIndex):
    if len(lines) >= ((blockIndex+1)*3):
        line = lines[blockIndex*3]
        line += lines[blockIndex*3+1]
        line += lines[blockIndex*3+2]
    else:
        line = ''

    return line

# file  - holds reference to existing file of all blocks. For efficiency keep the entire content in memory (lines variable)
file = open("file.txt", "r")
lines = file.readlines()
linesCount = len(lines)

# newFile holds reference to newly created file and it will have the resultant blocks after filtering
newFile = open("file_temp.txt","w")


# loop through all inputs and create a dictionary of all blocks to delete. This is done to have efficiency while removing the blocks with O(n) time

delDict = {}
for kkk in kkk_list:
    ip, port, name = re.split(":|,", kkk)
    tobedel = printInFormat(ip, port, name)
    delDict[tobedel] = 1

for i in range(linesCount / 3):
    block = getNextBlock(lines, i)
    if block in delDict:
        print 'Deleting ... '+block
    else:
        #write into new file
        newFile.write(block)

file.close()
newFile.close()

#You can drop the old file and rename the new file as old file

希望对您有所帮助！

Answer 2

让我指出您遗漏的小事。

for kkk in kkk_list:
    ip, port, name = re.split(":|,", kkk)
    tobedel = printInFormat(ip, port, name)  
    f = open("file.txt", "r+")
    d = f.readlines()
    f.seek(0)
    if kkk != "tobedel":
        f.write(YY)
f.truncate()
f.close()

您在循环内打开文件并在循环外关闭。文件对象超出范围。使用 with 自动为您处理上下文。
在循环中打开文件是个坏主意，因为它会创建很多文件描述符，消耗大量资源。
你写的时候从来没有提到什么是YY
你可以在这里删除行，因为你想一次删除多行，所以d = f.readlines()应该是d = f.read()

下面是更新后的代码。

#!/usr/bin/python
import argparse
import re
import string

p = argparse.ArgumentParser()
p.add_argument("input", help="input the data in format ip:port:name", nargs='*')  
args = p.parse_args()
kkk_list = args.input # ['192.168.1.10:80:name1', '172.25.16.2:100:name3']


def getStringInFormat(ip, port, name):
    formattedText = "HOST Address:{ip}:PORT:{port}\n"\
                    "mode tcp\n"\
                    "bind {ip}:{port} name {name}\n\n".format(ip=ip, 
                                                                port=port, 
                                                                name=name)

    return formattedText

# Writing the content in the file
# with open("file.txt", "a") as myfile:
#    for kkk in kkk_list:
#         ip, port, name = re.split(":|,", kkk)
#         myfile.write(getStringInFormat(ip, port, name))



with open("file.txt", "r+") as f:
    fileContent = f.read()

    # below two lines delete old content of file
    f.seek(0)
    f.truncate()

    # get the string you want to delete
    # and update the content
    for kkk in kkk_list:
        ip, port, name = re.split(":|,", kkk)

        # get the string which needs to be deleted from the file
        stringNeedsToBeDeleted = getStringInFormat(ip, port, name)

        # remove this from the file content    
        fileContent = fileContent.replace(stringNeedsToBeDeleted, "")

    # delete the old content and write back with updated one
    # f.truncate(0)
    f.write(fileContent)

# Before running the script file.txt contains 

# HOST Address:192.168.1.10:PORT:80
# mode tcp
# bind 192.168.1.10:80 name name1
#
# HOST Address:172.25.16.2:PORT:100
# mode tcp
# bind 172.25.16.2:100 name name3

# After running file.txt will be empty
# as we have deleted both the entries.

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