Python equivalent for HashMap

Python equivalent for HashMap

In Python, the equivalent of Java's HashMap is the dict (dictionary) data type. A dictionary is an unordered collection of key-value pairs, where each key must be unique. It allows you to store and retrieve values based on their associated keys efficiently.

Here's how you can create and use a dictionary in Python:

# Creating a dictionary my_dict = { 'name': 'John', 'age': 30, 'city': 'New York' } # Accessing values by key print(my_dict['name']) # Output: 'John' print(my_dict['age']) # Output: 30 # Modifying values my_dict['age'] = 31 # Adding a new key-value pair my_dict['country'] = 'USA' # Removing a key-value pair del my_dict['city'] # Checking if a key exists in the dictionary if 'name' in my_dict: print('Name is in the dictionary.') # Iterating through keys and values for key, value in my_dict.items(): print(f'Key: {key}, Value: {value}') # Dictionary length (number of key-value pairs) print(len(my_dict)) # Output: 3 (after removing 'city' and adding 'country')

Dictionaries are highly versatile and commonly used in Python for various purposes, including mapping, caching, and data organization. They are similar to Java's HashMap in the sense that they allow you to associate keys with values, and you can perform various operations like adding, updating, or removing key-value pairs as needed.

Examples

  1. Python dictionary as HashMap example

    • Description: Demonstrates how to use a Python dictionary as an equivalent of a HashMap.
    # Creating a HashMap equivalent using a dictionary hashmap = {'key1': 'value1', 'key2': 'value2', 'key3': 'value3'} # Accessing values from the HashMap print(hashmap['key2']) # Output: 'value2'

  2. Python defaultdict as HashMap example

    • Description: Illustrates how to use Python's defaultdict from the collections module as a HashMap.
    from collections import defaultdict # Creating a HashMap equivalent using defaultdict hashmap = defaultdict(lambda: 'default_value') hashmap['key1'] = 'value1' hashmap['key2'] = 'value2' # Accessing values from the HashMap print(hashmap['key2']) # Output: 'value2'

  3. Python dict() constructor for HashMap example

    • Description: Shows how to create a HashMap equivalent using the dict() constructor in Python.
    # Creating a HashMap equivalent using the dict() constructor hashmap = dict([('key1', 'value1'), ('key2', 'value2'), ('key3', 'value3')]) # Accessing values from the HashMap print(hashmap['key3']) # Output: 'value3'

  4. Python OrderedDict as LinkedHashMap example

    • Description: Demonstrates how to use Python's OrderedDict from the collections module as a LinkedHashMap, which maintains the order of insertion.
    from collections import OrderedDict # Creating a LinkedHashMap equivalent using OrderedDict linkedhashmap = OrderedDict([('key1', 'value1'), ('key2', 'value2'), ('key3', 'value3')]) # Accessing values from the LinkedHashMap print(linkedhashmap['key1']) # Output: 'value1'

  5. Python hash() function for hashing keys in a HashMap example

    • Description: Illustrates how to use Python's hash() function to hash keys in a HashMap.
    # Creating a HashMap equivalent using a dictionary with hashed keys key1 = hash('key1') key2 = hash('key2') key3 = hash('key3') hashmap = {key1: 'value1', key2: 'value2', key3: 'value3'} # Accessing values from the HashMap print(hashmap[key2]) # Output: 'value2'

  6. Python zip() function for creating HashMap from two lists example

    • Description: Shows how to use Python's zip() function to create a HashMap from two lists.
    # Creating a HashMap equivalent using zip() function keys = ['key1', 'key2', 'key3'] values = ['value1', 'value2', 'value3'] hashmap = dict(zip(keys, values)) # Accessing values from the HashMap print(hashmap['key3']) # Output: 'value3'

  7. Python custom class as HashMap keys example

    • Description: Demonstrates how to use a custom class as keys in a HashMap.
    # Creating a HashMap equivalent with custom class keys class Key: def __init__(self, name): self.name = name def __hash__(self): return hash(self.name) def __eq__(self, other): return self.name == other.name hashmap = {Key('key1'): 'value1', Key('key2'): 'value2', Key('key3'): 'value3'} # Accessing values from the HashMap print(hashmap[Key('key1')]) # Output: 'value1'

  8. Python frozendict for immutable HashMap example

    • Description: Illustrates how to use the frozendict library to create an immutable HashMap in Python.
    from frozendict import frozendict # Creating an immutable HashMap equivalent using frozendict hashmap = frozendict({'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}) # Accessing values from the immutable HashMap print(hashmap['key2']) # Output: 'value2'

  9. Python custom implementation of HashMap example

    • Description: Shows how to implement a custom HashMap class in Python.
    # Custom HashMap implementation class HashMap: def __init__(self): self.map = {} def put(self, key, value): self.map[key] = value def get(self, key): return self.map.get(key) # Usage my_map = HashMap() my_map.put('key1', 'value1') print(my_map.get('key1')) # Output: 'value1'

  10. Python Builtin type() for checking HashMap type example

    • Description: Demonstrates how to use Python's built-in type() function to check if an object is a HashMap.
    # Checking if an object is a HashMap hashmap = {'key': 'value'} if type(hashmap) == dict: print("It's a HashMap!")

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