Strings are built on characters, and each character has one length. Finding the length of a string means how many characters are there in the string.

You must count each character, including spaces and punctuation, So even if the string has spaces like “hello world”, the number of characters would be 11 because there’s a space between the two words.

Python provides a built-in len() function that returns the number of characters(including spaces and punctuation) in the string.

new_string = 'Leo Messi'

length_of_string = len(new_string)

print("Length of the string:", length_of_string)

# Output: Length of the string: 9

Empty String

If a string is empty, the length of that string is 0.

str = ""

print(len(str))

# Output: 0

Special Characters, like emojis or Unicode characters

If your string contains special characters like emojis (😊), that’s a single Unicode character. The len(😊) should return 1 because, in Python3, strings are Unicode by default.

str = "😊"

print(len(str))

# Output: 1

However, some Unicode characters are a combination of multiple code points. For example, some emojis are combinations, like flags or skin tone modifiers, or 👨🏾🚀. How about that?

If I have a string with a combined emoji, like “👨🏾🚀”, which represents an astronaut with a specific skin tone, it can have multiple code points, depending on its representation.

str = "👨🏾🚀"

print(len(str))

# Output: 3

You thought there were only 2 characters, but No, there are 3. That means counting characters might become complicated when using emojis.

Escape Characters

Your input string may contain escape characters like “\n” or newline characters. How will len() function judge that? Well, it will count as a single character. A string can have multiple escape characters.

str = "Hello\tWorld\n"

print(str)
# Output: Hello 	World

print(len(str))
# Output: 12

Here, \t counted as one character, and \n counted as one character. Total 2 special characters. The other 10 are normal characters. Hence, the total length is 12.

Alternate Approaches

Here are three alternate ways:

1. Using List Comprehension
2. Using reduce()
3. Using for loop

Approach 1: Using List Comprehension

The combination of List comprehension with the sum() function can iterate over the string and generate a sequence of 1s, one for each character. The sum of this sequence provides the total length of the string.

new_string = 'Leo Messi'

length_of_string = sum(1 for _ in new_string)

print("Length of the string:", length_of_string)

# Output: Length of the string: 9

Approach 2: Using reduce()

The reduce() function, combined with a lambda function, iterates over the string, incrementing a counter for each character encountered and final counter will be the size of the string.

from functools import reduce

new_string = 'Leo Messi'

length_of_string = reduce(lambda count, _: count + 1, new_string, 0)

print("Length of the string:", length_of_string)

# Output: Length of the string: 9

Approach 3: Using for loop

A for loop iterates over each character in the string, incrementing the count variable by 1 for each character.

new_string = 'Leo Messi'

count = 0
for x in new_string:
    count += 1

print("Length of the string:", count)

# Length of the string: 9

Why do we measure the size of a string?

Data validation

If you want to validate an input field like a username or password, you first need to determine its size. To do this, you can use the len() function.

username = input("Enter username: ")

if 3 <= len(username) <= 20:
    print("Valid username")
else:
    print("Username must be 3-20 characters")

# Output:
# Enter username: de
# Username must be 3-20 characters

Check for an empty input

If you want to ensure that your input is not empty, you should create an if condition based on its length and compare it to 0.

user_input = input("Enter text: ").strip()

if len(user_input) == 0:
    print("Input cannot be empty!")

# Output:
# Enter text:
# Input cannot be empty!

Encryption/Hashing

You can create a hashed or encrypted string by determining its length and pad some characters to hash it.

def pad_string(str, block_size):
    return str + '0' * (block_size - len(str) % block_size)


original = "kaynes"
padded = pad_string(original, 8)

print(padded)
# Output: kaynes00

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