Get length of dictionary in Python

Python provides multiple methods to get the length, and we can apply these methods to both simple and nested dictionaries. Let’s explore the various methods.

Using Len() Function

To calculate the length of a dictionary, we can use Python built-in len() method. It method returns the number of keys in dictionary.

d ={'Name':'Steve', 'Age':30, 'Designation':'Programmer'}
print(len(d))

3

Let's explore other methods of getting length of a dictionary in python:

Using List Comprehension

Another less common method is to use a list comprehension, which can also be used to count the number of keys in a dictionary.

Example:

d = {"a": 1, "b": 2, "c": 3}
length = len([key for key in d])
print(length)

3

Explanation:

• This method creates a list of keys using a list comprehension ([key for key in my_dict]), and len() is then used to count the number of keys.

Using sum() with 1 for each item

We can also use the sum() function to count the number of items in a dictionary by adding 1 for each key-value pair.

Example:

d = {"a": 1, "b": 2, "c": 3}
length = sum(1 for i in d)
print(length)

3

Getting length of nested dictionary

When working with nested dictionaries, we may want to count only the top-level keys or count the keys in nested dictionaries. If we want to get the length of the top-level dictionary, len() works just as it does with simple dictionaries.

d = {
    "person1": {"name": "John", "age": 25},
    "person2": {"name": "Alice", "age": 30},
    "person3": {"name": "Bob", "age": 22}
}
length = len(d)
print(length)

3

Explanation:

• d contains 3 top-level key-value pairs, so len() returns 3.

Using Loop to Count Items (Manual Counting)

Another method to count items in a dictionary, including nested dictionaries, is using a loop. For nested dictionaries, we can manually iterate through all the nested keys and values.

d = {
    "product1": {"name": "Laptop", "price": 800, "stock": 15},
    "product2": {"name": "Smartphone", "price": 500, "stock": 30},
    "product3": {"name": "Tablet", "price": 300, "stock": 25}
}
cnt = 0
# Loop through the top-level dictionary
for key, val in d.items():
    if isinstance(val, dict):  # Check if the value is a nested dictionary
        # Loop through the nested dictionary
        for i in val:
            cnt += 1  # Count each key in the nested dictionary
    else:
        cnt += 1  # Count the top-level keys
print(cnt)

9

Explanation:

• We iterate over each key-value pair in the top-level dictionary d.
• If the value is a nested dictionary (as in the case of "person1", "person2", and "person3"), we loop through that nested dictionary and count its keys (name and age).
• We also count the top-level keys (person1, person2, person3).
• The total count of items (keys) in the entire dictionary is 6 (3 top-level keys + 3 keys inside the nested dictionaries).

Using len() to get length of Keys, Values or Items

We can also use the len() function on the dictionary’s keys, values or items to determine the number of keys, values or key-value pairs.

d = {"a": 1, "b": 2, "c": 3}
# Number of Keys
length = len(d.keys())
print(length)
#  Number of Values
length = len(d.values())
print(length)
# Number of Items
length = len(d.items())
print(length)

3
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3