Noor Sohail
Will Gammerdinger
March 14, 2026
species list and what is it?--------------------------------------------------------------------------- IndexError Traceback (most recent call last) Cell In[8], line 2 1 # Access the fourth element of the species list ----> 2 species[3] IndexError: list index out of range
We only have 3 elements in our species list, so trying to access the fourth element with species[3] will result in an error. If you try to access an index that is out of range for a list, you will get an IndexError. This is because the indices for our species list only go up to 2 (since we have 3 elements, and indexing starts at 0).
"yeast" to the species list and print the updated list.species list using slicing?Hint: Recall that we can use negative indexing to access elements from the end of the list.
# Access the last two elements of the species list using slicing
species[-2:]
species[-2:len(species)]['corn', 'yeast']steps using the syntax list[start:stop:step]. This allows you to access every step-th element in the range from start to stop. How would you access every other element in the species list using slicing?corn in the genome_dict dictionary?---
title: "Data Structures - Answer Key"
author:
- Noor Sohail
- Will Gammerdinger
date: "2026-03-14"
license: "CC-BY-4.0"
editor_options:
markdown:
wrap: 72
---
```{python}
#| label: load_libraries_data
#| echo: false
# Load libraries and data
glengths = [4.6, 3000, 50000]
glengths.append(12000)
species = ["ecoli", "human", "corn"]
genome_dict = {
"ecoli": 4.6,
"human": 3000,
"corn": 50000,
"yeast": 12000
}
```
# Exercise 1
1. How would you access the fourth element of the `species` list and what is it?
```{python}
#| label: exercise_1
#| error: true
# Access the fourth element of the species list
species[3]
```
We only have 3 elements in our `species` list, so trying to access the fourth element with `species[3]` will result in an error. If you try to access an index that is out of range for a list, you will get an `IndexError`. This is because the indices for our `species` list only go up to 2 (since we have 3 elements, and indexing starts at 0).
2. Add `"yeast"` to the `species` list and print the updated list.
```{python}
#| label: exercise_2
# Append yeast to the species list
species.append("yeast")
print(species)
```
# Exercise 2
1. How might you access the last two elements of the `species` list using slicing?
*Hint: Recall that we can use _negative indexing_ to access elements from the end of the list.*
```{python}
#| label: exercise_3
# Access the last two elements of the species list using slicing
species[-2:]
species[-2:len(species)]
```
2. You can actually slice with `steps` using the syntax `list[start:stop:step]`. This allows you to access every `step`-th element in the range from `start` to `stop`. How would you access every other element in the `species` list using slicing?
```{python}
#| label: exercise_4
# Access every other element in the species list using slicing
print(species[::2])
print(species[0:4:2])
```
# Exercise 3
1. How would you access the genome length for `corn` in the `genome_dict` dictionary?
```{python}
#| label: exercise_5
# Access the value for the key "corn"
genome_dict["corn"]
```