如何用python中的最新值替换文本文件中的一行？

Question

I'm trying to assign a value to each image in a folder where the value can be anything from 1 to 6. The image is shown in a GUI and from there value (radio buttons 1 to 6) is chosen and written to a text file.

So, if I have image1, image2, and image3 in a folder and if I'm assigning values 4, 5, and 6 respectively to image1, image2, and image3 then my output file has the following:

image1 4
image2 5
image3 6

this is working perfectly with my code given. But I also added two buttons (next and previous) to the GUI so that the user can change their decisions by clicking those buttons.

I want to record the last value the user select for each image before exiting the GUI. That is, if a user select values 4, 5, and 6 respectively to image1, image2, and image3 and then later reassigns image1 with value 2, the expected output is:

image1 2
image2 5
image3 6

with my code, it is recording all values without checking if or if not it already exists. ie the output that I'm getting is:

image1 4
image2 5
image3 6
image1 2

My code is given below:

def storeoutput(self):
        x= str(self.path)+ " " + str(str(int(self.v.get())) + "\n"
        output = open("output.txt", 'a')
        output.write(x)
        output.close()

Answer 1

Question : Replace a line in a text file

Reference

• Live Demo - repl.it

• module-csv

  The csv module implements classes to read and write tabular data in CSV format.

• dict

  An associative array, where arbitrary keys are mapped to values.

• Tutorial - 5.5. Dictionaries

  Another useful data type built into Python is the dictionary

---

Note : A dict does not preserve the order by default, before Python 3.7!

1. File data

   CSV = """image1 4 image2 5 image3 6 """

2. Read the file contents in a dict

   import csv, io # with open('file.csv') as f: with io.StringIO(CSV) as f: mydict = dict(csv.reader(f, delimiter=' ')) print(mydict) >>>{'image1': '4', 'image2': '5', 'image3': '6'}

3. Update the value

   mydict['image1'] = '2'

4. Write the dict

    # with open('file.csv', 'w') as f: with io.StringIO() as f: csv.writer(f, delimiter=' ').writerows(((k, v) for k, v in mydict.items()))

   File content :

    print(f.getvalue()) image1 2 image2 5 image3 6

Answer 2

The approach would better if you handle it as dictionary rather than text files. Some steps below:

1. Create an initial dictionary while the questionnaire begins. (I am assuming it is a questionnaire)

question_dict = {}

2. Since, you would have control over the image_name and the options (1-6). You can store each question with image and the option in the dictionary as below:
   question_dict["image_name1"] = 4 question_dict["image_name2"] = 5

3. if the previous is clicked from the UI, you would get the already initialized dictionary from a file and rewrite the value of the already existing image_name
   question_dict
question_dict["image_name1"] = 2

4. Finally, you can save the entire dictionary, per user into a json which would then be easy to parse, or iterate the dictionary and save to any other format.

Code Snippet for understanding:

#Create a file with an user_id_timestamp for the question session.
#Initial set of questions in the dictionary
dictionary = {}
# 1: Q1 and option selected and next is pressed, save the record into dictionary
# and save dictionary to a  file.
dictionary["image1"] = 4
# Repeat - 1, but this time with load the existing dictionary and write the new key-val and save
dictionary["image2"] = 5
# Repeat
dictionary["image3"] = 6

#Previous is clicked hence true
prev_clicked = True
if prev_clicked:
    # Assuming user is at image4 and clicks previous
    # 1. Open the saved dictionary as a file.
    # Save the new option to the already existing key to the dictionary as below
    dictionary["image3"] = 4
    # Save the dictionary again, as Repeat