Table of Contents
What Is the Index of the First Element in a Python List and Why Is It Not 1?
Learn the fundamental rule of Python indexing: lists are zero-indexed, meaning the first element is always at index 0. Understanding this concept is crucial for accessing list items correctly and avoiding common off-by-one errors in your code.
Question
What is the index of the first element in a Python list?
A. 0
B. −1
C. 1
D. It varies by interpreter
Answer
A. 0
Explanation
Lists start at index 0.
The index of the first element in a Python list is always 0.
Python uses zero-based indexing for all its sequence types, including lists, tuples, and strings. This means the count starts at 0, not 1. The first element is at index 0, the second element is at index 1, and so on. For a list of length n, the last element will be at index n-1.
For example, in the list my_list = [‘apple’, ‘banana’, ‘cherry’]:
- my_list[0] returns ‘apple’.
- my_list[1] returns ‘banana’.
- my_list[2] returns ‘cherry’.
The other options are incorrect for the following reasons:
- An index of −1 (B) is used in Python for negative indexing, which allows you to access elements from the end of the list. An index of -1 specifically refers to the last element, not the first.
- An index of 1 (C) would refer to the second element in the list due to zero-based indexing. This is a common mistake for programmers coming from languages that use one-based indexing (like R or Lua).
- The indexing scheme does not vary (D); it is a fixed and fundamental part of the Python language specification.
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