The Python len() function is useful to find the length of an object. Or, say, it returns the total number of items (elements) in an object. If you are finding the string length, then the len() function returns the total number of characters.
In this section, we discuss how to use the Python len() function on strings, tuples, lists, dictionaries, Sets, Bytes, and range to find the length.
Python len() function syntax
The syntax of the len() function is as shown below.
len(Object_Name)
Parameter: Here, the object name can be a string, list, tuple, dictionary, or set whose length must be calculated. Whatever object is passed to the Python len() function, it calculates the length and returns the result.
Return Value: The len() function returns an integer indicating the total number of items in a given object.
Python len() function to find string length
When you use this Python function on a String object, it counts and returns the total number of characters (including spaces) in a string. Or, say, find the length of a string.
The syntax of the string len() function is
len(stringName)
As you can see, the len() function accepts a string as a parameter and returns the total number of characters in it, including white spaces and special characters.
In this example, we declared a string and assigned ‘Tutorial Gateway’ to it. Next, we utilized the len() function to find its length. Here, the Python len() function counts the total number of individual characters in it, including a white space, and returns 16 as the output.
a = 'Tutorial Gateway'
print(len(a))
16Similarly, If we use the len() function on an empty string, it returns 0 because there are no characters in it.
a = ''
print(len(a))
0TIP: Please refer to the Program to find the string length article to see the other options.
Python len() function to find list length
A list is the most common data structure, and finding its length is a common scenario. The built-in list len() function also helps you to find the total number of List items. The syntax of the list len() function is
len(listName)
Here, we must pass ”listName” as a parameter to find the total items in a given list. Unlike the strings, the Python len() function finds the total number of individual items in a list. It considers a single entry as one, whether it can be an individual item or a nested list.
To demonstrate the list len() function, we declared an integer list and applied the method on it. As you can see from the result, it returns the total number of items or elements in the given list.
n = [15, 20, 35, 40, 55, 60, 70]
print(len(n))
7Empty List
If we apply the Python len() function on an empty List to find its length, it returns 0 because there are no elements in it.
n = []
print(len(n))
0Using the len() function on a string list
Similarly, we used the len() function on a list containing the string elements (words). The len() function calculates the number of elements in a string list without any issue.
a = ['apple', 'mango', 'orange', 'cherry','banana']
print(len(a))
5Using the Python len() function on a nested list
When it comes to nested lists, people usually confuse the return value. If you observe the example below, we declared a list of lists where there are three sub-lists, each sub-list has two list items. Here, the len() function considers each nested list as one entry and returns 3 as the length.
a = [[1, 2], [3, 4], [5, 6]]
print(len(a))
6TIP: Please refer to the Program to find the list length article to see the other options.
Python len() function to find the tuple length
Similar to the lists, we can use the len() function on tuples to find the total number of items in them. The syntax of the tuple len() function is
len(tuple)
Here, the len() function considers each item in a tuple as 1. This example calculates the length of a Tuple, which means counting the total number of items in a tuple. First, we declared an integer Tuple and applied the len() function to return the number of items in an integer Tuple.
n = (10, 20, 30, 40, 50, 60, 70, 80, 90)
print(len(n))
9Similarly, we used the Python len() function in a tuple of string items, where each item is considered a single entity and counts the total number of strings in a tuple.
a = ('Banana', 'Orange', 'Blackberry', 'Apple')
print(len(a))
4TIP: Please refer to the Program to find the tuple length article to see the other options.
Python len function to find dictionary length
Apart from lists and tuples, we can use the len() function on collections such as dictionaries, sets, or frozen sets. The len() function on the Dictionary returns the length. Or calculates the total number of available items in a given Dictionary. The syntax of the dictionary len() function is
len(dictionayName)
As you can see from the syntax, the Python len() function accepts the dictionary name and returns the total number of key-value pairs (elements) in it.
In the example below, we declare a dictionary with integer keys and fruits as the values. Next, we utilized the len() function to find out the total number of key-value pairs in the dictionary.
a = {1: 'mango', 2: 'kiwi', 3: 'cherry'}
print(len(a))
3If we use the len() function on an empty dictionary, it will return 0 because there are no key-value pairs to count.
b = dict()
print(len(b))
0Similarly, we can use the Python len() function on mixed dictionary items. In the example below, we declared a dictionary with string and integer values. Next, the len() function finds the total number of elements (key-value pairs) in the mixed dictionary.
c = {'ID': 42, 'name': 'Kevin', 'age': 25, 1: 1200}
print(len(c))
4Python len() function to find the set length
The len() function also finds the total number of items in a set or the length. The syntax of the set len() function is
len(setName)
Here, we must pass the set name as the parameter value to find the total number of elements in a given set.
In the example below, we declared a numeric set with seven items. Within the print() statement, we utilized the len() function to find the total number of items in a set.
a = {125, 200, 350, 400, 505, 607, 760}
print(len(a))
7Similarly, the following example calculates the length of an asset with string items.
s = {'apple', 'mango', 'cherry', 'kiwi', 'orange', 'banana'}
print(len(s))
6TIP: Please refer to the Program to find the set length article for other options.
Python len() function to find the length of an array
In this example, we find the size of an array. First, we calculate the length of an empty array. Next, find the total items in an Integer and String array.
Arr = []
print(len(Arr))
ArrExample = [5, 12, 35, 22, 40, 5]
print("\n", ArrExample)
print(len(ArrExample))
stringArr = ['apple', 'cherry', 'kiwi', 'mango', 'orange', 'banana']
print("\n", stringArr)
print(len(stringArr))
How to find the byte length?
The Python len() function also allows you to find the Byte length, and this example returns the same.
b = b'Simple Example'
print("Bytes = ", len(b))
Bytes = 14Python len() function inside a for loop
In all the above examples, we have used the len() function to find the length of a list, tuple, set, string, and dictionary. However, we can use it inside the for loop to iterate over the list items from start to end index position.
In the example below, we declared a list to demonstrate the len() function inside a for loop. However, the process is the same for strings, tuples, etc. Here, the range() function iterates from the starting index position 0 and ends before the value returned by the len() function. If len(n) is 4, it stops at 3 because it is the last index position.
n = [10, 20, 30, 40]
for i in range(len(n)):
print('Index Position =', i, 'Value =', n[i])
Result
Index Position = 0 Value = 10
Index Position = 1 Value = 20
Index Position = 2 Value = 30
Index Position = 3 Value = 40The len function is not only about returning object size, but you can also find the range length. In this example, we declare a range from 4 to 10 and return the total number of elements between that range. To better understand, we used another example with a big range.
a = range(4, 10) print(len(a)) b = range(15, 109) print(len(b))
6
94Python len() function on a numpy ndarray
Apart from the regular objects and collections, we can use the len() function on numpy ndarray to find its length. In the example below, we have declared a numpy array and utilized the len() function to find the total number of items in it.
import numpy as np
n = np.array([11, 22, 33 ,44, 55])
print(len(n))
5Python len() function on pandas dataframe
In the example below, we have declared an employee’s details and converted it to a pandas DataFrame. Next, the len() function finds the total number of items in a pandas dataframe.
import pandas as pd
empDict = {'name': 'Miller', 'Age': 32, 'Job': 'Developer'}
df = pd.DataFrame(empDict.items())
print(df)
print(len(df))
0 1
0 name Miller
1 Age 32
2 Job Developer
3Python len() function alternatives
In the above section, we used the built-in common len() function to find the length of a list, string, tuple, dictionary, set, numpy array, and a data frame. However, there are alternatives to find the length of an object, such as using loops, enumerate, lambda, list comprehensions, etc.
Using a for loop
As we all know, the for loop is the most common way of iterating over the elements in an object. The for loop is helpful to iterate over lists, tuples, sets, dictionaries, or string characters.
In the following example, we will use a for loop to iterate over the list items and find their length. Here, the for loop iterates the list items from start to end. On each iteration, the length variable is incremented by 1, resulting in the total number of list items.
n = [9, 8, 7, 6, 5, 4]
length = 0
for i in n:
length += 1
print(length)
print(len(n))
6
6Using a while loop
In the following example, we used a while loop with a try and except block to find the length of an object and handle errors. Here, we defined a custom function and utilized the iter() function.
Within the function, we initialize the counter variable to 0, and it will return the length of a given object. The iter() function converts the given list, string, or any collection to an iterator object, which gives one item at a time.
As our idea is to pull all items in an object one after the other until there are no items, we used the while loop. Here, we have defined an infinite while loop with a True value. So, we must manually stop it inside the block.
The next() function reads the next element from the iterator object, and the count value is increased by 1. Once there are no items in the iterator, the StopIteration exception occurs, and the break statement will exit the loop.
def custom_length(a):
count = 0
i = iter(a)
while True:
try:
next(i)
count += 1
except StopIteration:
break
return count
n = [10, 20, 30, 40]
print(custom_length(n))
4If you replace the list with a string, it will print the length of the string. Please replace the line below.
n = [10, 20, 30, 40]
With the following line.
n = "hello it"
8Using list comprehension
If you are comfortable with list comprehensions, other than the Python len() function, it is the most reliable way to find the length of a string, list, or any other object. Here, we used the built-in sum() function to calculate the total number of characters (length) in a given string.
n = "hello world"
total = sum([1 for _ in n])
print(total)
11Using enumerate()
As we all know, when iterating over any object, the enumerate() function automatically runs the counter value. We don’t have to use a separate variable to store the count value; it can be done using the enumerate() function.
Here, enumerate(n, 1) means on each iteration, the enumerate reads one character (item) from a string and accumulates the counter value. The count variable holds the last index position, and it is the length of the string.
def custom_length(n):
count = 0
for count, _ in enumerate(n, 1):
pass
return count
a = "hello world!"
print(custom_length(a))
12Using functools reduce() function
We can use the reduce() function available in the functools module to find the length of an object. However, it is not recommended for use because of its complex nature and the use of lambda expressions. The built-in Python len() function is the better option.
In the example below, we declared an integer list and applied the reduce() function with a lambda expression. Here, on each iteration, the count value increments from index position 0.
from functools import reduce
n = (11, 22, 33, 44, 55)
total = reduce(lambda count, _: count + 1, n, 0)
print(total)
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