Python Dictionary Tips and Tricks You Should Always Remember

# Introduction

 
Dictionaries in Python are useful for everything from configs, JSON data, to API responses. Most beginners only learn the basics, like creating a dictionary, accessing a key, and updating a value. That's it. However, there's a lot more to dictionaries than that. In this article, we'll go through 7 tips that will make your code cleaner and more Pythonic. So, let's get started.

# Using .get() Instead of [] for Lookups

 
Let's say that you are working with a dictionary and you need to access a value. But what if the key is not there? Let's say we have a config dictionary and you try to print the "timeout" key like this:

config = {"debug": True, "verbose": False}
print(config["timeout"])

Output:

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
----> 2 print(config["timeout"])
KeyError: 'timeout'

This will fail. You will get a KeyError because "timeout" isn't in the dictionary. Instead, you should use the .get() method. It's safer and you can set a default value if the key is missing.

config = {"debug": True, "verbose": False}

print(config.get("timeout", 30))

Output:

30

This will print 30, which is the default value we set. However, if a missing key is a bug, use square brackets. You want the error to show up right away in that case.

# Using defaultdict for Grouping Data

 
If you're working with a list of words and you want to count how many times each word appears, you might code it like this:

words = ["apple", "banana", "apple", "cherry", "banana", "banana"]

counts = {}

for word in words:
    if word not in counts:
        counts[word] = 0
    counts[word] += 1

print(counts)

Output:

{'apple': 2, 'banana': 3, 'cherry': 1}

This works, but it's a bit verbose. Python's defaultdict makes it cleaner:

from collections import defaultdict

words = ["apple", "banana", "apple", "cherry", "banana", "banana"]

counts = defaultdict(int)

for word in words:
    counts[word] += 1

print(counts)

Output:

defaultdict(, {'apple': 2, 'banana': 3, 'cherry': 1})

Because we used defaultdict(int), Python automatically creates a default value of 0 whenever a missing key is accessed.

# Merging Dictionaries With the | Operator

 
In modern Python, the cleanest way to merge dictionaries is with the | operator.

defaults = {"color": "blue", "size": "medium"}
overrides = {"size": "large", "weight": "heavy"}

merged = defaults | overrides
print(merged)

Output:

{'color': 'blue', 'size': 'large', 'weight': 'heavy'}

When keys overlap, the dictionary on the right side wins. If you want to do in-place merging, you can use the |= operator:

defaults |= overrides
print(defaults)

Output:

{'color': 'blue', 'size': 'large', 'weight': 'heavy'}

# Unpacking Dictionaries into Function Arguments

 
Let's say you have a function and a dictionary, and their fields or keys match. Instead of passing the keys one by one, like name=data["name"], age=data["age"], you can pass everything using the ** double-asterisk operator. Let's create a user function and some dummy user data to understand it:

def create_user(name, age, role="viewer"):
    return {"name": name, "age": age, "role": role}

user_data = {
    "name": "David",
    "age": 33
}

# Normal Way
user = create_user(
    name=user_data["name"],
    age=user_data["age"],
    role=user_data["role"]
)

print(user)

Output:

{'name': 'David', 'age': 33, 'role': 'viewer'}

# Using **
print(create_user(**user_data))

Output:

{'name': 'David', 'age': 33, 'role': 'viewer'}

Note that the "Normal Way" example above will raise a >KeyError because user_data does not contain a "role" key. The ** unpacking approach correctly falls back to the function's default value for role, making it both cleaner and more robust.

# Using the Walrus Operator With Dicts

 
Python 3.8 introduced the walrus operator (:=), which lets you assign a value as part of an expression. This is really useful with dictionaries.

Let's say you have a dictionary and you want to get the user data and their name if they exist. This is typically how you would normally code it:

data = {
    "user": {
        "name": "Bryan",
        "email": "bryan@gmail.com"
    }
}

if data.get("user") is not None:
    user = data.get("user")
    name = user.get("name")

    print(name)

Output:

Bryan

This works, but it repeats the same dictionary lookup multiple times. You can replace it with the walrus operator (:=), which looks up and assigns the value in a single step:

if (user := data.get("user")) is not None:
    name = user.get("name")

    print(name)

Output:

Bryan

This is especially helpful when working with nested dictionary structures.

# Using TypedDict for Structured Data

 
Dictionaries are flexible, but that flexibility can sometimes become a problem. For example:

def greet(user):
    return f"Hello, {user['name']}!"

user = {
    "name": "Clair",
    "age": "thirty"
}

print(greet(user))

Output:

Hello, Clair!

This works at runtime, but there is a hidden problem: "age" is supposed to be a number, not a string. Python itself will not complain, which can lead to bugs later in larger projects. TypedDict makes the expected dictionary structure explicit:

from typing import TypedDict

class UserProfile(TypedDict):
    name: str
    age: int

def greet(user: UserProfile) -> str:
    return f"Hello, {user['name']}!"

Now tools like mypy can catch mistakes before the code runs:

user: UserProfile = {
    "name": "Clair",
    "age": "thirty",
}

print(greet(user))

Output:

test.py:15: error: Incompatible types (expression has type "str", TypedDict item "age" has type "int")  [typeddict-item]
Found 1 error in 1 file (checked 1 source file)

For more complex validation, tools like dataclasses or Pydantic are often better choices.

# Iterating Easily: .items(), .keys(), .values()

 
Python dictionaries have many built-in methods for iteration: .items(), .keys(), and .values(). Most developers know about them, but don't use them as often as they should. They might loop over a dictionary like this:

scores = {
    "David": 92,
    "Bryan": 87,
    "Clair": 95
}

for name in scores:
    print(name, scores[name])

Output:

David 92
Bryan 87
Clair 95

That works. But it's not the best way — it does an extra dictionary lookup every time through the loop. Python's .items() method is cleaner:

for name, score in scores.items():
    print(name, score)

Output:

David 92
Bryan 87
Clair 95

It returns both the key and value together, which avoids repeated lookups and makes the code more readable. If you only need the keys, use .keys() instead. Similarly, if you only need the values, use .values().

# Wrapping Up

 
Python dictionaries look simple at first, but learning a few key patterns can make your code much cleaner. You can use this link to learn more about the functions associated with Python dictionaries. Features like .get(), defaultdict, unpacking, and TypedDict help reduce repetitive code and make your programs more reliable.
 
 

Kanwal Mehreen is a machine learning engineer and a technical writer with a profound passion for data science and the intersection of AI with medicine. She co-authored the ebook "Maximizing Productivity with ChatGPT". As a Google Generation Scholar 2022 for APAC, she champions diversity and academic excellence. She's also recognized as a Teradata Diversity in Tech Scholar, Mitacs Globalink Research Scholar, and Harvard WeCode Scholar. Kanwal is an ardent advocate for change, having founded FEMCodes to empower women in STEM fields.