What is the method for replacing strings in Python?

There are several methods for replacing strings in Python.

1. The replace() function in Python is an in-built function used to replace a substring in a string with another substring. Its syntax is as follows: new_string = old_string.replace(old_substring, new_substring). Here, old_string is the original string, old_substring is the substring to be replaced, new_substring is the substring to replace it with, and new_string is the new string after replacement. The replace() function returns a new string, while the original string remains unchanged.
2. The sub() function in Python’s re module is used to replace a substring in a string using a regular expression. The syntax is as follows:

   import re
   new_string = re.sub(pattern, new_substring, old_string)

   Where pattern is a regular expression that matches the substring to be replaced, new_substring is the replacement substring, old_string is the original string, and new_string is the resulting string after the replacement. The sub() function returns a new string without modifying the original string.

3. By using string slicing and concatenation: If you only need to replace a certain substring within a string, you can achieve this by using string slicing and concatenation. The specific steps are as follows: new_string = old_string[:start_index] + new_substring + old_string[end_index+1:]. Here, old_string is the original string, start_index and end_index are the starting and ending indexes of the substring to be replaced, new_substring is the new substring after replacement, and new_string is the new string after replacement. It is important to note that in the slicing operation [start_index:end_index] is a left-closed and right-open interval, so we need to use end_index+1 as the ending index for slicing. This method will return a new string without modifying the original string.

These methods are suitable for various string replacement scenarios, and the choice of method can be based on actual needs.