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How to Count Keys in a Python Dictionary

This guide explains how to get the number of keys (which is the same as the number of key-value pairs) in a Python dictionary.

We'll cover the most direct method, using len(), and briefly discuss other less common approaches.

The most straightforward and efficient way to count the number of keys in a dictionary is to use the built-in len() function directly on the dictionary:

my_dict = {
    'name': 'Tom Nolan',
    'age': 25,
    'tasks': ['dev', 'test']
}

result = len(my_dict)  # Directly on the dictionary
print(result)  # Output: 3
  • len(my_dict): This directly returns the number of key-value pairs in the dictionary. This is the best way to get the count.

Using len(my_dict.keys()) (Redundant)​

You might see code that uses len(my_dict.keys()). This works, but it's redundant:

my_dict = {'id': 1,  'name': 'Tom Nolan'}

print(my_dict.keys())       # dict_keys(['id', 'name']) # Creates a "view object"
print(len(my_dict.keys()))  # Output: 2
  • my_dict.keys(): This returns a view object that represents the dictionary's keys. View objects are efficient, but you don't need to explicitly create one just to get the count.
  • The result will be the same as with just passing the dictionary to len()

Using a for Loop (Inefficient)​

You could use a for loop to count keys, but this is highly inefficient and unnecessary:

my_dict = {
    'name': 'Tom Nolan',
    'age': 25,
    'tasks': ['dev', 'test']
}

count = 0
for key, value in my_dict.items():
    count += 1

print(count)  # Output: 3

  • The dict.items() method returns a new view of the dictionary's items.

  • This code manually iterates through the dictionary and increments a counter. len(my_dict) does the same thing, but much faster and more clearly. Avoid this approach for simply counting keys.

Counting Keys that Satisfy a Condition​

If you need to count keys based on some condition (e.g., keys whose values are greater than a certain number), use a generator expression with sum():

my_dict = {
    'a': 1,
    'b': 10,
    'c': 100,
}

count = sum(1 for key, value in my_dict.items() if value > 5)
print(count)  # Output: 2
  • sum(1 for ...): This is a concise way to count. The generator expression yields 1 for each key-value pair that meets the condition, and sum() adds them up.

Checking if a Dictionary is Empty​

To check if a dictionary is empty, you can use len(my_dict) == 0, or, more simply, just use the dictionary itself in a boolean context (an empty dictionary is falsy):

my_dict = {}

if len(my_dict) == 0:
    print('dict is empty') #Output: dict is empty
else:
    print('dict is not empty')

# More concisely:
if not my_dict:  # Empty dictionaries are "falsy"
    print('dict is empty') # Output: dict is empty

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