Discover Python Hashmap: The Key Technology You Need

A hashmap is a data structure that can be used to store data, implement different data structures like sets and caches and retrieve data quickly if necessary. They store data in a key-value format, and they’re very useful to engineers and programmers because they make it easy to search for keys and specific values when working with particularly large datasets, saving them a lot of time. Hashmaps map keys to different value pairs and use a function that computes an index value containing the elements you need. In Python, hashmaps or hash tables are implemented through the dictionary data type. 

Let’s look at an example of how this works: if you work with a large dataset like a hospital database, you have to keep track of all of the information pertaining to different patients and employees. When you need to find a specific element within this database, a hashmap is useful because it helps you retrieve information about a person quickly and also compare present data against previous values. 

A hashmap is generally more efficient than an array because it’s easier to insert and retrieve data. Using hashing to store data makes accessing and inserting information more efficient. An array, on the other hand, has to be searched sequentially in order to find a specific element, and this can be very time consuming if you’re working with a large amount of information. 

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Hash Functions in a Hashmap

A hash function uses a key as input and outputs a hash value or a hash. Hash functions are important because you can use the same input and the function will always give you the same output, meaning that the hashmap will be able to learn where a specific key-value pair needs to be stored within the map. Basically, this means organizing data and important information seamlessly, and it also makes it easier to retrieve and manipulate information. 

Hash functions are used in hash maps because they allow maps to quickly and efficiently find key-value pairs within the map by applying the hash function we mentioned earlier to return a particular hash value, and then use that value to determine where that key-value pair needs to be stored within the map. 

Adding Data to A Hashmap

If you want to add data to a hashmap in Python, you can use the update () method to take a dictionary as an argument and add all of its key-value pairs to the hashmap. 

Let’s look at how this works: 

patient_list = {}

patients = {

   "Sally": "001",

   "Peter": "002",

   "Tom": "003",

   "Jill": "004",

   "Grace": "005"}

patient_list.update(patients)

print(patient_list)

# {'Sally': '001', ‘Peter’: '002', ‘Tom’: '003', ‘Jill’: '004', ‘Grace’: '005'}

Dictionaries in Python: Curly Braces, Dict Constructor and Fromkeys Methods

A dictionary is also referred to as a hashmap in other programming languages, and it’s the unordered grouping of key-value pairs in Python. We have already seen why this is a preferred method for storing and retrieving data. Now, let’s take a look at how to create a dictionary in Python, including how to set up an empty dictionary, add and remove key-value pairs and access, retrieve and manipulate data within dictionaries. 

In order to create a dict in Python, you can use curly braces, the dict() constructor and the fromkeys() method. Curly braces are one way to create a dictionary in Python, and you can enclose a comma-separated list of key-value pairs in curly braces to set up these dictionaries. Use a colon and a comma to separate each pair of key-value pairs from the rest and set up your lists. 

Let’s take the following example based on the healthcare scenario we used earlier: 

MyDict = {1: "sally", 2: "peter", 3: "tom"}

We set up a dictionary MyDict with three key-value pairs:

1: "sally", 2: "peter", and 3: "tom". Keys are integers and values are strings here. 

The dict() constructor method produces a dictionary from an iterable of key-value pairs that serves as input. A list of tuples and arguments can be used to pass in the key-value pairs. You can create a dictionary with key-value pairs and pass them as arguments to the dict() constructor, and you can also create a dictionary using a list of tuples containing the key-value pairs you used before. Here, you can pass the list as an argument to the dict() constructor which will output a dictionary with the same key-value pairs. The dict() constructor can also be used if you need to create an empty dictionary by not passing any arguments, leaving it blank. 

Finally, the fromkeys() method is used to create a dictionary by selecting different keys from a sequence and then setting the values to default values. The first argument in the fromkeys() method is a list of keys, and the second argument, which is optional, is the value assigned to each specific key after it’s been set. Values will be set to None automatically if you opt out of the second argument. 

If you need to delete something in Python from a hashmap, you can use the del keyword to remove an element of the key-value pair. You can also use the pop() method of a dictionary object to remove a specific key-value pair from the dictionary. This takes the key of what you need removed as an argument and returns the value associated with that specific key. 

We’ve covered hashmaps and why they’re important, going over how to use them by creating dictionaries through different methods. Start seeing for yourself how hashmaps can make a huge difference to the way you store, retrieve and process data.