反转 Python 中文本文件每行的最后 4 个字符 3

Question

I am trying to move the last 4 characters from each end of a line of a text file at the front of the line.

For instance I have the following line: 6c6d6e6f707172737475767778797a7b10050

and I want the last 4 digits to get in the front of the line so I have the following code to do that:

import sys
import re
import os

def rearrange(word):
 if word.endswith('0'):         
     word = word[-4] + word[-3] + word[-2] + word[-1] + word[:-4]    
 print(word)
 return word

rearrange('6c6d6e6f707172737475767778797a7b10050')

I get the following output, hence so far so good, it works:

00506c6d6e6f707172737475767778797a7b1

However, when I try to do it for a small file with an iteration loop. Say the text file to read from is with the following lines:

6c6d6e6f707172737475767778797a7b10050
8d6d6e6f707172737475767778797a7b10020
9a6d6e6f707172737475767778797a7b10030

I want to work the same way but it I cannot get it to work. There is something obvious that is happening that I cannot see it, can someone spot it and help me out here please?

import sys
import re
import os

def rearrange(word):
     if word.endswith('0'):         
         word = word[-4] + word[-3] + word[-2] + word[-1] + word[:-4]    
     print("print while the routine is executed:")
     print(word)
     return word     

file_write = open (r"reversed-test_text1.txt",'wt')

with open(r"test_text1.txt") as file_read:
    for line in file_read:        
        r = rearrange(str(line))
        file_write.write(r)
     
file_read.close()
file_write.close()

f = open("reversed-test_text1.txt", 'r')
print('Print the 4-char reversed text:')   
print(f.read())

When I execute it I get the following which is not what I wanted:

Print the 4-char reversed text:
6c6d6e6f707172737475767778797a7b10050
8d6d6e6f707172737475767778797a7b10020
9a6d6e6f707172737475767778797a7b10030

Does anyone have any idea why? It must be dead simple but I fail to see it (not that experienced in Python either).

Answer 1

I think the problem is, that by reading the lines from the file, you have a \n in the end of each line. By your check for the zero in the rearrange -method, you are simply skipping your rearranging.

Answer 2

The if word.endswith('0'): condition is not satisfied, because each line ends with a newline character ( '\n' ).

To make it work as you expect, you might rewrite the loop as follows:

with open(r"test_text1.txt") as file_read:
    for line in file_read:        
        r = rearrange(line.rstrip())
        file_write.write(r + os.linesep)

The .rstrip() method trims the whitespaces characters from the end of the string.

The os.linesep is the default line separator of the current platform.