Question

以下功能是较大程序的一部分，旨在让用户“喜欢”一部电影并在电影文本文件中存储该值（通过递增）。奇怪的是，它在第一次迭代中工作正常（将其读入列表，更改值，将其写入文件），但在第二次迭代时，会发生错误。

该文件名为“films.txt，内容为：

    0,Genre,Title,Rating,Likes
    1,Sci-Fi,Out of the Silent Planet,PG,0
    2,Sci-Fi,Solaris,PG,0
    3,Sci-Fi,Star Trek,PG,0
    4,Sci-Fi,Cosmos,PG,0
    5,Drama,The English Patient,15,1
    6,Drama,Benhur,PG,0
    7,Drama,The Pursuit of Happiness,12,0
    8,Drama,The Thin Red Line,18,0
    9,Romance,When Harry met Sally,12,0
    10,Romance,You've got mail,12,0
    11,Romance,Last Tango in Paris,18,0
    12,Romance,Casablanca,12,0

此特定功能的代码如下：注意：idnumber是指每部电影的idnumber。例如，StarTrek的id号是3。

def likeafilm(x,username):
#prompt the user to enter the ID number they require
   idnumber=int(input("To confirm, please enter the number of the film you wish to like:"))
   #create a list which stores and displays all the data in the films txt file
   with open("films.txt",mode="r", encoding="utf8") as f:
      allfilms=[]
      reader=csv.reader(f)
      for row in reader:
         allfilms.append([element.strip() for element in row])

         #print(allfilms)
      print("print the third film", allfilms[3])
      print("print the second film", allfilms[2])
      print("print the current film selected", allfilms[idnumber])
      print("print the like for current film", allfilms[idnumber][4])

      allfilms[idnumber][4]=str(int(allfilms[3][4])+1) #this succesfully increments the record in the runtime list by 1
      print(allfilms) #this confirms the update - this now needs to be written to file.

   with open("films.txt","w") as f:
      writer=csv.writer(f)
      writer.writerows(allfilms)

   print("******BACK TO VIEWING FILMS SELECTION***********")
   watchfilms(username)

在第一次迭代，或第一次运行程序时，它工作正常！ 1增加（对于喜欢的人），一切都很好。发生的错误如下，第二次......

    print("print the like for current film", allfilms[idnumber][4])
    IndexError: list index out of range

更新代码

def likeafilm(x,username):
#prompt the user to enter the ID number they require
   idnumber=int(input("To confirm, please enter the number of the film you wish to like:"))
   #create a list which stores and displays all the data in the films txt file
   with open("films.txt",mode="r", encoding="utf8") as f:
      allfilms=[]
      reader=csv.reader(f)
      for row in reader:
         allfilms.append([element.strip() for element in row])

         #print(allfilms)
      print("print the third film", allfilms[3])
      print("print the second film", allfilms[2])
      print("print the current film selected", allfilms[idnumber])
      print("print the like for current film", allfilms[idnumber][4])

      allfilms[idnumber][4]=str(int(allfilms[3][4])+1) #this succesfully increments the record in the runtime list by 1
      print(allfilms) #this confirms the update - this now needs to be written to file.

   with open("films.txt","w") as f:
      writer=csv.writer(f)
      #writer.writerows(allfilms)
      allfilms.append([element.strip() for element in row])
      writer.writerows(allfilms)

   print("******BACK TO VIEWING FILMS SELECTION***********")
   watchfilms(username)

正如Apollo在下面提到的那样，我可以看到发生了什么（错误），但不知道如何修复它。它适用于第一次迭代，因为文件是正确的（没有空格）。然而，在SECOND迭代中，文件已被覆盖，并且它似乎对文件的内容做了一些事情。第二次出现这个错误：

    print("print the like for current film", allfilms[idnumber][4])
  IndexError: list index out of range

我尝试了这部电影5（英国病人 - 顺便说一句很棒的电影），虽然它第一次更新了它，并且喜欢增加到“1”，第二次，它没有。

我也尝试将文件编写器更改为“wb”而不是“w”，但也出现了以下错误：

writer.writerows(records)
TypeError: 'str' does not support the buffer interface

Answer 1

你有正确的想法，但我会把它分成两个功能，一个用于增加电影，一个用于用户互动。另外，您在调用内置函数open（）时尝试指定＆＃39; encoding＆＃39;，这不是有效参数。

import csv

films_file = "films.txt"

def like_film(x):
    with open(films_file,mode="r") as f:
        reader = csv.reader(f)
        records = [row for row in reader]
    for rec in records:
        if int(rec[0]) == x:
            rec[-1] = str(int(rec[-1]) + 1)
    with open("films.txt","wb") as f:
        writer=csv.writer(f)
        writer.writerows(records)

def user_like_film(username):
    x = int(input("Enter the ID of the film you wish to like: "))
    like_film(x)
    watchfilms(username)

Answer 2

找到答案：

在Python 2中，需要使用'wb'打开文件，如您所建议的那样，而不是'w'。

然而，我使用Python 3.在Python 3中，所需的语法略有不同。需要使用附加参数打开文件，即：newline =''而不是。

以下示例：

# Python 2
with open('filmsfile.txt', 'wb') as f:
    writer = csv.writer(f)

# Python 3
with open('filmsfile.txt', 'w', newline='') as f:
    writer = csv.writer(f)

从列表到文件写入更改的值，第二次迭代不起作用，Python

2 个答案: