来自.txt文件的Python列表

Question

I`m trying to create primitive dictionary (or list) in Python with basic functions that I learned from book (Mark Summerfield).

Here is my question.

All works as I need, but I had a problem with writing strings to the file.

This is a piece of my code:

  word = input("New word is: ") #adding new word
  if word:
       word.strip() #erasing new str from any symbols
       x = len(word)
       numeration = str(count) + ". " 
       word = word[:0] + numeration + word[0:] # =to sort as list
       word = word[:x] + ",\n" # =adding shift to the end of str
       file = open("test.txt", "a") # =wriing to the file 
       file.write(word)
       file.close()
       count += 1

Problem shows itself in the output:

======================== RESTART: /home/z177/test.py ========================
Type word to add word, type nothing to read dict, ^D\Z to quit
New word is: currently raining
New word is: currently not
New word is: 
1. currently rain,
2. currently ,

It is overwriting the last 3 symbols in the string.

I've solved this problem by replacing

word[:x] + ",\n" 

with

word + ",\n"

I am still interested why the code is replacing these 3 symbols when I add new symbols to the end of the string.

Can you explain this?

Answer 1

The issue is created in this line:

word = word[:x] + ",\n" # =adding shift to the end of str

You need to remember that variable word isn't contain your word any more. You have there for example "0. word" there.

So you have to update x - line count to get correct results in your file.

Answer 2

The length of word has increased after inserting numeration , so x holds the value of the old length before the update. You should move the line where x is assigned after the update:

numeration = str(count) + ". " 
word = numeration + word[0:] # length of word changes here
x = len(word)
word = word[:x] + ",\n"

Or stick to using word = word + ",\\n" which is less verbose and still does the same thing.

---

The entire logic can however be simplified into the following:

word = numeration + word + ',\n'  

Answer 3

Your problem is that you set x to be the length of the input word, but then add numeration to the string, making it several characters longer (three characters, in the case of a single-digit count ). If you were to change

word = word[:x] + ",\n" # =adding shift to the end of str

to

word = word[:len(word)] + ",\n"

You should get the correct result.

Unrelated to your issue, the code you presented is very un-Pythonic, and when you've mastered the logic of the program I'd take a look at refactoring, using with open('test.txt', 'a') as file: over the explicit file.close() and using str.format() over concatenation.