Welcome! This tutorial is designed to teach you how to find the last occurrence of a character in a list in Python. Essential for many data analysis and string manipulation tasks, Python provides several ways to accomplish this task and we will guide you through one of the simplest yet practical methods.
So, whether you are new to programming, or an expert Pythonista wanting to hone your skills, this tutorial is going to be beneficial for you.
Step 1: Defining the Problem
Consider a list of characters, let’s say,
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['a', 'b', 'c', 'a', 'b', 'c', 'a'] |
We want to find the index of the last occurrence of the character ‘a’ in this list. The answer in this case should be 6. Let’s learn how to find this programmatically using Python.
Step 2: Python List’s Built-in reverse() and index() Methods
The reverse() inbuilt function of the Python list reverses the order of items. The index() method returns the index of the first occurrence of an item. These are the two methods we are going to utilize to find our solution.
First, we will reverse the list and then use the index method to find the first (which is technically the last) occurrence of the target character. However, since the list is now reversed, we must subtract the found index from the length of the list to get the original position of the last occurrence of the character.
Here is what this looks like in the code:
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def find_last_occurrence(lst, char): # Reverse the copy of the list rev_list = lst[::-1] # Find the index of the last occurrence of char return len(lst) - 1 - rev_list.index(char) |
You can use the function above with any list and character like this:
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find_last_occurrence(['a', 'b', 'c', 'a', 'b', 'c', 'a'], 'a') |
It will return 6, which is the correct index of the last occurrence of ‘a’ in the list.
Complete Python code:
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def find_last_occurrence(lst, char): rev_list = lst[::-1] return len(lst) - 1 - rev_list.index(char) print(find_last_occurrence(['a', 'b', 'c', 'a', 'b', 'c', 'a'], 'a')) |
Output:
6
Conclusion
In this tutorial, you have learned how to find the last occurrence of a character in a list in Python using a simple, yet effective, method of reversing a list and using the index() method.
Although Python has many different ways to achieve the same result, this approach is straightforward and easy to follow, making it suitable for Python learners of all levels.