How do I merge two dictionaries in a single expression in Python?
Merging Dictionaries in One Go for Cleaner, More Efficient Python Code
When working with Python, merging two dictionaries often comes up, especially when you’re aggregating data, updating configurations, or combining results from different computations. Historically, you might have relied on multiple lines of code, using methods like update()
or iterating through keys. Modern Python, however, offers elegant ways to merge dictionaries in a single expression, resulting in cleaner, more maintainable code.
Utilizing the Dictionary Unpacking Operator (**
)
If you’re using Python 3.5 or newer, you can take advantage of dictionary unpacking. The **
operator unpacks a dictionary’s key-value pairs, allowing you to combine multiple dictionaries into a single new one:
dict1 = {"a": 1, "b": 2} dict2 = {"b": 3, "c": 4} merged = {**dict1, **dict2}
In this expression, merged
now contains {"a": 1, "b": 3, "c": 4}
. Notice that the value of b
was overwritten by dict2
, as it appears later in the unpacking sequence. This approach is both concise and clear: you see precisely how the dictionaries are combined, making your code easier to understand and maintain.
Using the Union Operator (|
) in Python 3.9+
For those using Python 3.9 or above, an even more streamlined approach is available. The dictionary union operator |
merges two dictionaries and returns a new one:
dict1 = {"a": 1, "b": 2} dict2 = {"b": 3, "c": 4} merged = dict1 | dict2
This line achieves the same result as the unpacking method but in a more visually intuitive manner. It clearly states the intent: merged
is the union of dict1
and dict2
. If a key is present in both dictionaries, the right-hand dictionary’s value takes precedence.
Why Merge Dictionaries in a Single Expression?
- Conciseness: Reducing code from multiple lines to a single, self-contained expression makes your logic more readable and easier to follow.
- Maintainability: When you or another developer revisit the code, it’s immediately clear how data is combined—no guesswork or separate updates required.
- Better Debugging: With fewer steps involved, there’s less room for errors or confusion. Should an issue arise, it’s simpler to pinpoint where and why it happened.
Performance Considerations
While merging dictionaries in a single expression is clean and Pythonic, both the **
unpacking and the |
operator create a new dictionary rather than updating one in place. If you’re performance-sensitive and need to avoid extra copies, consider using dict.update()
on an existing dictionary. For most general use-cases, though, these new single-expression techniques strike the perfect balance between elegance and efficiency.
Strengthen Your Python Skills
Whether you’re merging dictionaries, handling files, or crafting complex data pipelines, a solid foundation in Python’s core features and best practices is essential. If you’re just starting out or want to refine your skills:
- Grokking Python Fundamentals: Perfect for beginners, this course helps you understand Python’s core concepts, from basic data types and control flow to more advanced topics like dictionary unpacking.
If your goals extend beyond the fundamentals to excelling in technical interviews:
- Grokking the Coding Interview: Patterns for Coding Questions: Learn proven coding patterns that prepare you for common interview challenges.
- Grokking Data Structures & Algorithms for Coding Interviews: Build a solid grasp of DSA concepts, ensuring you’re ready for a variety of problem-solving scenarios.
Also, explore the DesignGurus.io YouTube channel for free, insightful videos that complement your learning journey—covering coding best practices, system design principles, and interview tips.
In Summary
Merging two dictionaries in a single expression is a hallmark of Python’s evolving elegance and readability. Whether you choose dictionary unpacking (**
) or the union operator (|
), you’ll write code that’s both concise and intuitive. As you become more proficient in Python, these small improvements add up, helping you craft more efficient, maintainable applications that shine in both production settings and interview scenarios.