为什么在python中写入文件不起作用？

Question

The idea behind the following code is that the if the variable crop is already contained within the .txt file the variable quantity will be added on to the end of the same line as crop . This is my attempt at doing this, however it doesn't work: you really need to run it to understand, but, essentially, the wrong section of the list is added to, an ever expanding series of '/' appear and the line breaks disappear. Does anyone know how to modify this code so it functions properly?

What should be outputted:

Lettuce 77 88 100
Tomato 99

What actually is outputted:

["['\\n', 'Lettuce 77 \\n88 ', 'Tomato 88 ']100 "]

Code:

def appendA ():

 with open('alpha.txt', 'r') as file_1:
  lines = file_1.readlines()

  for line in lines:
    if crop in line:
        index = lines.index(line)
        line = str(line + quantity + ' ')
        lines [index] = line
        newlines = str(lines)

        #The idea here is that the variable quantity is added onto the end
        # of the same row as the entered crop in the .txt file.


        with open('alpha.txt', 'w') as file_3:
            file_3.write (newlines)

def appendB ():

 with open('alpha.txt', 'a') as file_2:

    file_2.write ('\n')
    file_2.write (crop + ' ')
    file_2.write (quantity + ' ')

crop = input("Which crop? ")
quantity = input("How many? ")

with open('alpha.txt', 'a') as file_0:

 if crop in open('alpha.txt').read():
    appendA ()
 else:
    appendB ()

Answer 1

newlines = str(lines) # you convert all lines list to str - so you get default conversion

and also you should replace whole file if you want to write in the middle

And you can also get read of appendB, because you still check every line and your code anyway is not optimal in terms of performance :)

from os import remove, close

def appendA(filename, crop, quantity):

    result = []
    exists = False
    with open(filename, 'r') as file_1:
        lines = file_1.readlines()

    for line in lines:
        if not crop in line:
            result.append(line)
        else:
            exists = True
            result.append(line.strip('\n') + quantity + '\n')


    if not exists:          
        with open(filename, 'a') as file_2:
            file_2.write ('\n' + crop + ' ' + quantity + ' ')
    else:
        tmp_file = filename + '.tmp'
        with open(tmp_file, 'w') as file_3:
            file_3.write(result)
            remove(filename)
            move(tmp_file, filename)

Answer 2

Let's start! Your code should look something like this:

def appendA():
    with open('alpha.txt', 'r') as file_1:
        lines = []

        for line in file_1:
            if crop in line:
                line = str(line.rstrip("\n") + quantity + "\n")
            lines.append(line)

        #The idea here is that the variable quantity is added onto the end
        # of the same row as the entered crop in the .txt file.
        with open('alpha.txt', 'w') as file_3:
            file_3.writelines(lines)


def appendB():
    with open('alpha.txt', 'a') as file_2:
        file_2.write('\n')
        file_2.write(crop + ' ')
        file_2.write(quantity + ' ')

crop = "Whichcrop"
quantity = "+!!!+"

with open('alpha.txt') as file_0:
    if crop in file_0.read():
        print("appendA")
        appendA()
    else:
        print("appendB")
        appendB()


 with open('alpha.txt', 'a') as file_0:
     if crop in open('alpha.txt').read():
         appendA ()
     else:
         appendB ()

Also you make several mistakes. This line "with open('alpha.txt', 'a') as file_0:" open file with context for append in the end of file, but you dont use variable file_0. I think it's extra. On next step you opened file for check "crop in open('alpha.txt').read()", but never close it.

["['\\n', 'Lettuce 77 \\n88 ', 'Tomato 88 ']100 "] You get such a output because, you use write instead of writelines: with open('alpha.txt', 'w') as file_3: file_3.write (newlines)

Also you write in the file after each iteration, better to form a list of strings and then write to file.

Answer 3

1. "str(lines)": lines is list type, you can use ''.join(lines) to convert it to a string.
2. "line in lines": "line" end with a "\\n"
3. Code indent error: "line newlines = ''.join(lines)" and the follow
4. "if crop in lines" is mistake, if crop named "AA" and "AABB", the new input "AA" with return true, the quantity will be appended to all lines including "AA" ,not only the "AA" line.

    def appendA():
        with open('alpha.txt', 'r') as file_1:
            lines = file_1.readlines()

            for line in lines:
                if crop in line:
                    index = lines.index(line)
                    line = str(line.replace("\n", "") + ' ' + quantity + '\n')
                    lines[index] = line
            newlines = ''.join(lines)

            # The idea here is that the variable quantity is added onto the end
            # of the same row as the entered crop in the .txt file.
            with open('alpha.txt', 'w') as file_3:
                file_3.write(newlines)


    def appendB():
        with open('alpha.txt', 'a') as file_2:
            file_2.write("\n")
            file_2.write(crop + ' ')
            file_2.write(quantity + ' ')


    crop = input("Which crop? ")
    quantity = input("How many? ")

    with open('alpha.txt', 'a') as file_0:
        if crop in open('alpha.txt').read():
            appendA()
        else:
            appendB()