How to Find the Length of Strings, Lists, and Dictionaries in Python | Rustcode

How to Find the Length of Strings, Lists, and Dictionaries in Python

Measuring the length of objects is a fundamental task in Python, whether you're working with strings, lists, or dictionaries. Python's built-in len() function makes it easy to get the number of characters, elements, or key-value pairs in these data types. This article explains how to use len() with strings, lists, and dictionaries, with syntax, code examples, outputs, and best practices.

What is len() in Python?

Definition: len() is a built-in Python function that returns the number of items in an object.
Use Cases: Works with strings, lists, dictionaries, tuples, sets, and more.
Benefits: Simple, efficient, and works consistently across many data types.
References: [3][6][8]

01. Find the Length of a String

To get the number of characters in a string (including spaces, punctuation, and special characters), use len() with the string as its argument.

text = "Hello, World!"
print(len(text))

Output:

Explanation:

len(text) returns the number of characters in the string, including spaces and punctuation.
Works with empty strings (returns 0) and any Unicode characters.
References: [1][2][3][4][5][6][7][8]

02. Find the Length of a List

To find the number of elements in a list, pass the list to len().

fruits = ["apple", "banana", "cherry"]
print(len(fruits))

Output:

Explanation:

len(fruits) returns the count of elements in the list.
Works for lists of any data type, including mixed types and nested lists.
References: [2][3][6][8]

03. Find the Length of a Dictionary

For dictionaries, len() returns the number of key-value pairs.

person = {"name": "Alice", "age": 30, "city": "New York"}
print(len(person))

Output:

Explanation:

len(person) counts the number of key-value pairs in the dictionary.
Empty dictionaries return 0.
References: [6][8]

04. len() with Other Data Types

len() also works with tuples, sets, and other collections:

numbers = (1, 2, 3, 4)
print(len(numbers))  # Tuple

unique_items = {10, 20, 30}
print(len(unique_items))  # Set

Output:

4
3

Explanation:

Returns the number of items in tuples and sets, just like for lists.
For unsupported types (like integers or booleans), len() raises a TypeError.
References: [2][3][6][8]

05. Manual Length Calculation (for loop)

You can also calculate length manually by iterating and counting items. This is educational but less efficient than using len().

my_list = [10, 20, 30, 40]
count = 0
for item in my_list:
    count += 1
print(count)

Output:

Explanation:

Increments a counter for each item in the collection.
Helps understand how len() works internally.
References: [7]

06. Comparing len() Usage in Python

Type	What len() Returns	Example	Notes
String	Number of characters	len("hello") → 5	Includes spaces, punctuation
List	Number of elements	len([1, 2, 3]) → 3	Works for any list
Dictionary	Number of key-value pairs	len({"a": 1, "b": 2}) → 2	Keys must be unique
Tuple	Number of elements	len((1, 2, 3)) → 3	Immutable sequence
Set	Number of unique elements	len({1, 2, 3}) → 3	Unordered, unique items

Conclusion

Python's len() function is the standard way to find the length of strings, lists, dictionaries, and other collections. It is simple, reliable, and works across many data types. Use len() whenever you need to measure the size of a collection or string in your Python programs.

Tip: Always use len() for length checks, and remember it works differently depending on the data type!