使用csv閱讀器從列表中刪除行並列出python

Question

在SO上也有類似的問題，但沒有涉及我需要的細節。

我有以下代碼，試圖根據指定的用戶輸入刪除文件中的一行。該方法是

1. 讀取文件到列表
2. 刪除列表中的相關行（理想情況下，而列表中的閱讀？）
3. 過寫文件。

對於最好的解決方案（對於初學者，用於教學/學習目的），我希望得到一些指導和評論，以便在csv中執行這種簡單的Python刪除/編輯操作讀者。

代碼

""" ==============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? 

文件內容：

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

基於下面的答案，我有這個，但是當它覆蓋文件，它不會正確更新列表，不知道爲什麼。

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() 

它似乎正確地打印更新文件（作爲列表），因爲它刪除了輸入的用戶名。但是在寫入文件時，它只會向文件打印一個用戶名。

有什麼想法，我可以接受最終答案？

Answer 1

if username not in updatedlist:

對我來說應該是：

if row[0] != username:

然後在第二循環中，您寫updatedlist到CSV文件。 我會在閱讀的時候將所有內容都寫在另一個文件中，然後最後刪除舊文件並將其替換爲新文件，這使得它只有一個循環。

編輯：

updatedlist=row與updatedlist.append(row)替換：第一個裝置重寫updatedlist與一個行，而第二個裝置增加一個行到它。

writerow寫入一行，然後給它一個行列表。 改爲使用writerows，您的寫作功能將起作用。

你幾乎完成了這一切，這是我的目標。 其他一些答案已經給你更好的（更快，更乾淨...）的方式，所以我不會。

Answer 2

這樣的事情應該可以做到，使用csv模塊。由於您已將表格數據與定義的列結構化在一起，因此您應該使用DictReader和DictWriter來讀寫您的文件;

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() 

這將打開輸入文件，過濾出其中的用戶名是等於所需的用戶名要刪除任何條目，並寫入留下哪些條目背出輸入文件，覆蓋什麼已經存在。

Answer 3

我推薦這種方法：

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() 

所有的文件中的行被讀入lines。然後我回到f.seek(0)的文件起始位置。此時，用戶會被要求輸入一個用戶名，然後在回寫該文件之前用它來檢查每一行。如果該行包含指定的用戶名，則不會寫入，因此會「刪除」該用戶名。最後我們用f.truncate()刪除任何多餘部分。我希望這有助於，如果你有任何問題不要猶豫，問！

Answer 4

我試着堅持你的代碼：（編輯：不優雅，但是儘可能接近到OPS代碼）

""" ==============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) 

不過，我會建議使用numpy的還是熊貓

Answer 5

而對於另一個答案：寫入一個新文件，然後重命名它！

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()