Replacing a character from a certain index [duplicate]

Question

How can I replace a character in a string from a certain index? For example, I want to get the middle character from a string, like abc, and if the character is not equal to the character the user specifies, then I want to replace it.

Something like this maybe?

middle = ? # (I don't know how to get the middle of a string)  if str[middle] != char:     str[middle].replace('') 

Answer 1

As strings are immutable in Python, just create a new string which includes the value at the desired index.

Assuming you have a string s, perhaps s = "mystring"

You can quickly (and obviously) replace a portion at a desired index by placing it between "slices" of the original.

s = s[:index] + newstring + s[index + 1:] 

You can find the middle by dividing your string length by 2 len(s)/2

If you're getting mystery inputs, you should take care to handle indices outside the expected range

def replacer(s, newstring, index, nofail=False):     # raise an error if index is outside of the string     if not nofail and index not in range(len(s)):         raise ValueError("index outside given string")      # if not erroring, but the index is still not in the correct range..     if index < 0:  # add it to the beginning         return newstring + s     if index > len(s):  # add it to the end         return s + newstring      # insert the new string between "slices" of the original     return s[:index] + newstring + s[index + 1:] 

This will work as

replacer("mystring", "12", 4) 'myst12ing'