Question

对此有类似的问题，但没有一个涉及我要求的具体细节。

我有以下代码，它试图根据指定的用户输入删除文件中的行。方法是

将文件读入列表
删除列表中的相关行（理想情况下，在列表中读取时？）
覆盖文件。

我希望有一些指导和关于最佳解决方案的评论（对于初学者，用于教学/学习目的），用csv阅读器在python中进行这种简单的删除/编辑。

代码

""" ==============TASK
1. Search for any given username
2. Delete the whole row for that particular user

e.g.
Enter username: marvR
>>The record for marvR has been deleted from file.
"""

import csv

#1. This code snippet asks the user for a username and deletes the user's record from file.

updatedlist=[]
with open("fakefacebook.txt",newline="") as f:
  reader=csv.reader(f)
  username=input("Enter the username of the user you wish to remove from file:")
  for row in reader: #for every row in the file
      if username not in updatedlist:
        updatedlist=row #add each row, line by line, into a list called 'udpatedlist'
        print(updatedlist)

 #delete the row for the user from the list?
#overwrite the current file with the updated list?

文件内容：

username,password,email,no_of_likes
marvR,pass123,marv@gmail.com,400
smithC,open123,cart@gmail.com,200
blogsJ,2bg123,blog@gmail.com,99

更新

根据下面的答案，我有这个，但是当它覆盖文件时，它不会正确地更新列表，不确定原因。

import csv
def main():
    #1. This code snippet asks the user for a username and deletes the user's record from file.
    updatedlist=[]
    with open("fakefacebook.txt",newline="") as f:
      reader=csv.reader(f)
      username=input("Enter the username of the user you wish to remove from file:")
      for row in reader: #for every row in the file
          if row[0]!=username: #as long as the username is not in the row .......
            updatedlist=row #add each row, line by line, into a list called 'udpatedlist'
            print(updatedlist)
    updatefile(updatedlist)

def updatefile(updatedlist):
    with open("fakefacebook.txt","w",newline="") as f:
        Writer=csv.writer(f)
        Writer.writerow(updatedlist)
        print("File has been updated")


main()

它似乎正确打印更新的文件（作为列表），因为它删除了输入的用户名。但是在将此文件写入文件时，它只会在文件中输入一个用户名。

有任何想法，我可以接受最终答案吗？

Answer 1

if username not in updatedlist:

对我来说应该是：

if row[0] != username:

然后在第二个循环中，将更新列表写入csv文件。我会在读取时将所有内容写入另一个文件中，然后最后删除旧文件并将其替换为新文件，这使其只有一个循环。

编辑：

将updatedlist=row替换为updatedlist.append(row)：第一个意味着用一行覆盖updatedlist，而第二个意味着再添加一行。

writerow写一行，然后给它一个行列表。使用writerows代替您的写作功能。

你差不多完成了所有这一切，这是我的目标。其他一些答案已经为你提供了更好（更快，更清洁......）的方法，所以我不会。

Answer 2

使用csv模块，你应该这样做。由于您使用已定义的列构建了表格数据，因此您应使用DictReader和DictWriter来读取/写入文件;

import csv

with open('fakefacebook.txt', 'r+') as f:
    username = input("Enter the username of the user you wish "
                         "to remove from file:")
    columns = ['username', 'password', 'email', 'no_of_likes']

    reader = csv.DictReader(f, columns)
    filtered_output = [line for line in reader if line['username'] != username]

    f.seek(0)
    writer = csv.DictWriter(f, columns)
    writer.writerows(filtered_output)
    f.truncate()

这将打开输入文件，过滤掉用户名等于要删除的所需用户名的任何条目，并将剩余的条目写入输入文件，覆盖已经存在的内容。< / p>

Answer 3

我推荐这种方法：

with open("fakefacebook.txt", 'r+') as f:
    lines = f.readlines()
    f.seek(0)

    username = input("Enter the username of the user you wish to remove from file: ")
    for line in lines:
        if not username in line.split(',')[0]:  # e.g. is username == 'marvR', the line containing 'marvR' will not be written
            f.write(line)

    f.truncate()

文件中的所有行都会被读入lines。然后我用f.seek(0)返回文件的起始位置。此时，系统会要求用户输入用户名，然后用户在写回文件之前检查每一行。如果该行包含指定的用户名，则不会写入，因此“删除”它。最后，我们使用f.truncate()删除任何多余的内容。我希望这有帮助，如果您有任何问题请不要犹豫！

Answer 4

我试图坚持你的代码:(编辑：不优雅，但尽可能接近OP代码）

""" ==============TASK
1. Search for any given username
2. Delete the whole row for that particular user

e.g.
Enter username: marvR
>>The record for marvR has been deleted from file.
"""

import csv

#1. This code snippet asks the user for a username and deletes the user's record from file.

updatedlist=[]
with open("fakefacebook.txt",newline="") as f:
  reader=csv.reader(f)
  username=input("Enter the username of the user you wish to remove from file:")
  content = []
  for row in reader: #for every row in the file 
     content.append(row)

# transpose list  
content = list(map(list, zip(*content)))
print(content)
index = [i for i,x in enumerate(content[0]) if x == username]
for sublist in content:
  sublist.pop(index[0])

print(content)

# transpose list  
content = list(map(list, zip(*content)))

#write back
thefile = open('fakefacebook.txt', 'w')
for item in content:
  thefile.write("%s\n" % item)

但我建议使用numpy或pandas

Answer 5

另一个答案是：写一个新文件，然后重命名它！

import csv
import os

def main():
    username = input("Enter the username of the user you wish to remove from file:")
    # check it's not 'username'!

    #1. This code snippet asks the user for a username and deletes the user's record from file.
    with open("fakefacebook.txt", newline="") as f_in, \
            open("fakefacebook.txt.new", "w", newline="") as f_out:
        reader = csv.reader(f_in)
        writer = csv.writer(f_out)
        for row in reader: #for every row in the file
            if row[0] != username: # as long as the username is not in the row
                writer.writerow(row)
    # rename new file
    os.rename("fakefacebook.txt.new", "fakefacebook.txt")

main()

使用csv reader从文件中删除行并列出python

5 个答案: