Noor Sohail
Will Gammerdinger
March 14, 2026
species list and what is it?--------------------------------------------------------------------------- IndexError Traceback (most recent call last) Cell In[2], 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?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
3. How might you access the last two elements of the `species` list using slicing?
::: callout-tip
# 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)]
```
4. 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
5. 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"]
```