Question

我有以下代码，其中的注释解释了输出和所需的输出。我似乎无法访问（或理解逻辑）如何访问列表中的不同字段。

def viewrecs(username):
    username = (username + ".txt")
    with open(username,"r") as f:
      fReader=csv.reader(f)
      for row in fReader:

         for field in row:

            #print(field) #this prints everything in the file
            #print(row) #this also prints everything in the file
            #print(row[0])  #this also prints everything!!!!!!
            #print(field[0]) #this prints the first ELEMENT in each row, namely the "["
            #How do I access the first field of each column (the genre, like SCI-FI, or Romance)

有问题的文件是基于用户用户名的文本文件。内容如下：

"['Sci-Fi', 'Blade Runner']"
"['Sci-Fi', 'Star Trek']"
"['Sci-Fi', 'Solaris']"
"['Sci-Fi', 'Cosmos']"
"['Drama', ' The English Patient']"
"['Sci-Fi', 'Out of the Silent Planet']"
"['Drama', ' The Pursuit of Happiness']"
"['Drama', ' The English Patient']"
"['Drama', ' Benhur']"
"['Drama', ' Benhur']"

关于如何访问列字段（例如科幻，戏剧等）的答案以及解释将非常感谢。

我想打印整个第一列......即SCI-FI，SCI-FI，SCI-FI，DRAMA等......我需要将它们理想地读入列表以便它们可以被操作在列表中

根据以下答案之一，如果问题是关于数据首先写入文件的方式，则将此数据写入文件的代码/函数如下：

def viewfilmfunction(x,username):
   #open the file as student file (variable)
   print(username, ":You are about to view Film:", x, "Enter the selection     ID number of the film again to confirm viewing")
   with open("films.txt","r") as filmsfile:
        #prompt the user to enter the ID number they require
        idnumber=input("Enter the ID number you require:")
        #call upon our reader (this allows us to work with our file)
        filmsfileReader=csv.reader(filmsfile)
        #for each row that is read by the Reader    
        for row in filmsfileReader:
            #and for each field in that row (this does it automatically for us)
            for field in row:
                #if the field is equal to the id number that is being searched for
                if field ==idnumber:
                    #print the row fields (genre and title) corresponding to that ID number
                   #create a list which contains the relevant fields in the row.
                  viewedlist=[row[1],row[2]]
                  print("You have viewed:", viewedlist)
   with open("fakeflixfile.txt","r")as membersfile:
      #Open Reader
            membersfileReader=csv.reader(membersfile)
            for row in membersfileReader:              
               for field in row:
                  if field==username:

                     #Open Writer to append to file -this time it looks for the file stored by that username
                     with open("%s.txt" % username,"a") as membersfile:

                        membersfileWriter=csv.writer(membersfile)
                        #Use the writer to append the viewedlist to the appropriate member's user file. 
                        membersfileWriter.writerow([viewedlist])

FAKEFLIXFILE.txt内容

username13022,Username@123,user,name1,2/02/3022,user Road,US455P,Mle,Nothing,username1@hotmail.com AugustineSalins1900.txt,Augstine@123,Augustine,Salins,5/02/1900,Hutchins Road,CRBBAAA,Male,Theology,augustine@hotmail.com JosieBletchway3333,Bb@123,Josie,Bletchway,29/02/3333,Bletch Park,BB44AA,Female,Encryption,blecth@hotmail.com JoeBloggs.0.0,Joe@Bloggs12,Joe,Bloggs,0.0.0.0,0 Road,00000,Male,Joe Blogs,joe@hotmail.com

更新：我现在更改了txt文件（基于用户名），以便生成的输出不会生成列表：

Drama, The English Patient

Drama, Benhur

Sci-Fi,Cosmos

然而，在跑步时：

def viewrecs(username):
   #pass
   username = (username + ".txt")
   with open(username,"r") as f:
          fReader=csv.reader(f)
          for row in fReader:
             print(eval(row)[0])

错误仍然存在：

    print(eval(row)[0])
    TypeError: eval() arg 1 must be a string, bytes or code object

Answer 1

因为您的文件不是有效的CSV文件。它看起来更像是一系列JSON对象。文件中的每一行都用双引号括起来。因此，CSV阅读器将其视为单个列。这就是你在行[0]

中得到的原因

这是由您编写文件的方式引起的。下面的行告诉CSV编写器写一个对象，该对象是包含两个值的列表

membersfileWriter.writerow([viewedlist])

你真正想要的是告诉CSV编写器写多个对象。将您的行更改为此行，无需将其括在方括号中：

membersfileWriter.writerow(viewedlist)

然后您可以使用它来阅读您的文件：

with open(username,"r") as f: fReader=csv.reader(f) for row in fReader: print (row) # print entire row print (row[0]) # print just the first field

访问列表Python中每行的第一列

1 个答案: