Learn how to Replace the Second Occurrence of a Character in a String
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The video explains a Python function replace_second designed to replace the second occurrence of a specified character in a string. Here’s a line-by-line explanation of the code, enhanced for tutorial purposes:
def replace_second(string, old, new): - This line declares a function named replace_second. This function is designed to take three arguments:
string: This will be the original text you want to modify.old: This is the specific character you want to find and replace. We’re aiming for the second time it appears.new: This is the character that will be put in place of the second occurrence of old.first_index = string.index(old) - Here, we use the built-in index() method of strings. This method searches through the string and returns the index (the position) of the very first time it encounters the old character. This index is stored in the variable first_index.index = first_index + 1 - Now, we take the index of the first occurrence and add 1 to it. We store this new value in a variable also named index. This is a clever trick: by starting our next search after the first occurrence, we ensure we find the second one.before = string[:index] - We now slice the original string. This line takes all the characters from the beginning of the string up to (but not including) the position indicated by our current index. This creates a new string called before containing everything before where the second occurrence (or potentially the position after the first) starts.after = string.index(old, index) - Instead of simply slicing the rest, this line is crucial for correctly identifying the second occurrence. We use the index() method again, but this time with a second argument: our calculated index. This tells Python to start searching for the old character from this position onwards. This guarantees we find the index of the second occurrence (if it exists) and store it back into the index variable.before_second = string[:index] - Now we slice the string again, this time up to the actual index of the second occurrence.after_second = string[(index + 1):] - We slice the string from the position after the second occurrence to the very end.return before_second + new + after_second - Finally, we build the result. We take the part of the string before the second occurrence (before_second), then we insert our new character, and then we append the part of the string after the second occurrence (after_second). This modified string is then returned by the function.print(replace_second("yellow", "l", "x")) - This line shows how to use the replace_second function. We provide the string “yellow”, tell it to find “l”, and replace it with “x”. The output of this line will be “yexlow” because the second “l” has been replaced.Tutorials, Roadmaps, Bootcamps & Visualization Projects