Dictionary Operations in Python

This article explains dictionary operations in Python.

You can learn how to define dictionaries, basic operations, how to merge dictionaries, and more, by looking at sample code.

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Dictionary Operations in Python

In Python, a dictionary (dict) is a collection that manages data as key-value pairs. Unlike lists, you access them by keys, not by position, making lookups and updates efficient.

Definition of a Dictionary

1my_dict = {
2    'apple': 3,
3    'banana': 5,
4    'orange': 2
5}
6print(my_dict)

• A dictionary is written with curly braces {}, separating keys and values with a colon :.

Accessing Keys and Values

1print(my_dict['apple'])  # Output: 3

• Specify a key to retrieve its corresponding value.

Adding or Updating Items in a Dictionary

1my_dict['pear'] = 4  # Add a new item
2my_dict['apple'] = 5  # Update an existing item
3print(my_dict)

• You can add a new key-value pair or update the value for an existing key.

Removing Items from a Dictionary

1del my_dict['banana']
2print(my_dict)

• Using del deletes the specified key and its value.

1value = my_dict.pop('orange')  # Remove the item 'orange' and get its value
2print(value)
3print(my_dict)

• Alternatively, use the pop method to remove an item and retrieve its value.

Checking for Key Existence in a Dictionary

1if 'apple' in my_dict:
2    print("Apple is in the dictionary.")

• Use the in operator to test whether a key exists in the dictionary.

Iterating Through a Dictionary

1for key, value in my_dict.items():
2    print(f"{key}: {value}")

• Use the items() method to loop through the dictionary and process its keys and values. The items() method lets you iterate over both keys and values.

Retrieving Only Keys or Values from a Dictionary

1keys = my_dict.keys()
2values = my_dict.values()
3print(keys)
4print(values)

• Use the keys() method to retrieve only the keys or the values() method to retrieve only the values.

Copying a Dictionary

1new_dict = my_dict.copy()
2print(new_dict)

• Use the copy() method to create a copy of a dictionary. The copy() method creates a shallow copy. To copy nested dictionaries, you can use copy.deepcopy().

Merging Dictionaries

1dict1 = {'apple': 3, 'banana': 5}
2dict2 = {'orange': 2, 'pear': 4}
3combined_dict = dict1 | dict2
4print(combined_dict)

• From Python 3.9 onwards, the | operator can be used as a new way to merge dictionaries.

1dict1.update(dict2)
2print(dict1)

• On older versions, use the update() method.

Summary

Dictionaries are a fundamental tool for data management in Python programming. They manage data as key-value pairs and offer many advantages, including fast access, flexible updates, and easy merging. By mastering their use, you will be able to write more efficient and flexible code.

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