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CPE 202 Lab 8 Solved

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In this lab, you will implement a hash table that uses separate chaining for its collision resolution strategy.

1 Hash Table
1.1 Our Implementation

In this lab, your “chains” will be Python lists. So, the HashTable class will be a Python list (the table) of Python
lists (the separate chains).
The hash table will be initialized with two parameters, the initial capacity of the hash table, and a hash function
to use for the keys.

By default, we will use Python’s builtin hash function, but we want to support creating a hash
table that uses a different hashing function.
To create a list of empty lists, we will do something like:
table = [[] for _ in range(10)]

We can then add to a given chain by appending to the relevant list. So, if we want to insert the key-value pair (16,
‘cat’) into the table at index 6, we would do:
table[6].append((16, ‘cat’))
And then the table would look like:
[[], [], [], [], [], [], [(16, ‘cat’)], [], [], []]

1.2 Operations

You will implement the following operations for a hash table:
• insert This function takes a hash table, a key, and a value as arguments. The function will insert the key-value
pair into the hash table based on the hash value of the key mod the table size.
If they key being inserted is already present in the hash table, the old value will be replaced by the new given
value. We should not end up with duplicate keys in the table.

If the insert would cause the load factor of the hash table to exceed 1.0, your hash table should double in
capacity and reinsert all of the values from the old table into the new table.
• get_item This function takes a hash table and a key as arguments. The function will retrieve the value for
the given key, and will return the value.

If the given key is not present in the hash table, this function will raise a KeyError.
• contains This function takes a hash table and a key as arguments. The function will return True if the key
is present in the hash table, and False otherwise.

• remove This function takes a hash table and a key as arguments. The function will remove the key-value pair
from the hash table and return the pair (as a tuple).
If the given key is not present in the hash table, this function will raise a KeyError.
CPE 202 Lab 8, Page 2 of 2

• size This function takes a hash table as an argument and returns the number of key-value pairs that have
been inserted into the hash table.
• keys This function takes a hash table as an argument and returns a list of all of the keys in the table.
• load_factor This function takes a hash table as an argument and returns the load factor of the hash table.
• _contents This function takes a hash table as an argument and returns the internal hash table array. You
may find this useful for testing.

Note that the leading underscore is not a typo. It’s generally bad practice for a function like this to exist, and
so we’re using the Python standard practice of a leading underscore to mean that it’s not meant to be used
directly by “users” of your HashTable structure. You should only be using this for testing.

2 Testing

As mentioned in the syllabus, your code is periodically graded prior to the deadline and you will receive automated
feedback based on the results of my tests. But, in order to receive any feedback, your tests much provide 100% test
coverage of the code you are submitting.

If you do not have 100% coverage, this is the only feedback you will receive.
100% test coverage means that every line of your code is run at some point in some test. Imagine if that weren’t the
case.

That means that you have a line of code (or multiple lines of code) that could do anything, and you’d never
know. You never tested them!
Your tests will go in files named hash_table_tests.py.

3 GitHub Submission

Push your finished code back to GitHub. Refer to Lab 0, as needed, to remember how to push your local code.