5 Best Ways to Use Set in Python for Pangram Checking

💡 Problem Formulation: A pangram is a sentence that contains every letter of the alphabet at least once. The classic example is: “The quick brown fox jumps over the lazy dog.” In this article, we aim to check if a given string is a pangram using Python. The input is a string and the desired output is a boolean indicating whether the string is a pangram or not.

Method 1: Using Set with Lowercase Comparison

This method involves converting the input string to lowercase, then creating a set of the alphabet and a set of the characters in the string. If the alphabet set is a subset of the characters set, the string is a pangram. This is effective because sets cannot contain duplicate elements, making it easy to compare unique characters.

Here’s an example:

import string

def is_pangram(sentence):
    alphabet = set(string.ascii_lowercase)
    return alphabet.issubset(set(sentence.lower()))

print(is_pangram("The quick brown fox jumps over the lazy dog"))

Output: True

This code snippet defines a function is_pangram() that takes a string, transforms it to lowercase, then creates a set of unique characters from the sentence. It compares this set to a predefined set of all lowercase letters in the English alphabet. The method returns True if the set of the alphabet is a subset of the sentence character’s set, indicating a pangram.

Method 2: Using Set Intersection

In this method, we create sets of the alphabet and the sentence’s characters and check for their intersection. If the intersection size is 26 (number of letters in the English alphabet), then the sentence is a pangram. This method is direct and leverages set theory principles.

Here’s an example:

import string

def is_pangram(sentence):
    return len(set(string.ascii_lowercase).intersection(set(sentence.lower()))) == 26

print(is_pangram("Pack my box with five dozen liquor jugs"))

Output: True

The function is_pangram() computes the intersection of the sets representing the sentence’s characters and the alphabet. If the length of the resulting set is 26, it means that all the alphabet’s letters are present in the sentence. Hence, it returns True for pangrams.

Method 3: Using Set Difference

With this approach, we subtract the characters set of the sentence from the alphabet set. If the result is an empty set, the provided sentence has every alphabet letter, thus it is a pangram. This subtraction method is intuitive, as it directly removes seen characters from the required set.

Here’s an example:

import string

def is_pangram(sentence):
    return set(string.ascii_lowercase) - set(sentence.lower()) == set()

print(is_pangram("Cwm fjord bank glyphs vext quiz"))

Output: True

The is_pangram() function compares the set of the alphabet with the set derived from the sentence after converting all characters to lowercase. If the difference is an empty set, it implies all alphabet letters are used; thus, it returns True.

Method 4: Using Set Length Comparison

This technique first removes non-alphabetic characters from the sentence and then compares the length of the set of characters with the total number of unique letters in the alphabet. A match indicates the sentence is a pangram.

Here’s an example:

import string

def is_pangram(sentence):
    sentence_chars = [char for char in sentence.lower() if char.isalpha()]
    return len(set(sentence_chars)) == 26

print(is_pangram("Jinxed wizards pluck ivy from the big quilt"))

Output: True

The code defines a is_pangram() function where it first filters alphabetic characters from the sentence and converts them to lowercase. Then it checks if the set of these characters is equal in length to the number of unique letters in the alphabet.

Bonus One-Liner Method 5: Set Comprehension

This compact one-liner uses set comprehension to create a set from the input string stripped of non-alphabet characters, immediately evaluates its length, and compares it to the alphabet length—all within a function return statement.

Here’s an example:

import string

def is_pangram(sentence):
    return len({char for char in sentence.lower() if char in string.ascii_lowercase}) == 26

print(is_pangram("Quick zephyrs blow, vexing daft Jim."))

Output: True

The provided code introduces a one-liner is_pangram() function using a set comprehension that filters and lowers the case of characters in the input sentence. It checks if the size of this set equals the total number of unique alphabet letters.

Summary/Discussion

• Method 1: Using Set with Lowercase Comparison. Strengths: Straightforward logic. Weaknesses: May have extra processing due to two set operations.
• Method 2: Using Set Intersection. Strengths: Utilizes set theory effectively. Weaknesses: Can be less intuitive for some programmers.
• Method 3: Using Set Difference. Strengths: Directly signifies missing elements. Weaknesses: Inefficient if set difference is large.
• Method 4: Using Set Length Comparison. Strengths: Filters out non-alphabetic characters before comparison. Weaknesses: Multiple iterations over sentence.
• Method 5: Set Comprehension. Strengths: Compact and elegant. Weaknesses: May sacrifice readability for brevity.