5 Best Ways to Check If a String Is a Pangram in Python

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πŸ’‘ Problem Formulation: A pangram is a sentence that contains every single letter of the alphabet at least once. For example, the sentence “The quick brown fox jumps over a lazy dog” is a pangram. This article explores different methods to check if a given string is a pangram using Python. The input is the string to be checked, and the desired output is a Boolean value indicating whether the input string is a pangram or not.

Method 1: Using Set and ASCII Lowercase

This method involves checking if the set of characters in our string, once converted to lowercase, is equal to the set of characters in the English alphabet. We use Python’s built-in set type to store unique characters and the string constant ascii_lowercase from the string module to represent the English alphabet.

Here’s an example:

import string

def is_pangram(s):
    return set(string.ascii_lowercase) <= set(s.lower())

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

Output: True

This code snippet defines a function called is_pangram that takes a string s as its parameter. The function converts the string to lowercase, creates a set of characters from it, and checks if all the characters from ascii_lowercase are in the set. This comparison yields True if the string is a pangram.

Method 2: Using Alphabet Check with ASCII Value Range

This approach manually creates a list of all alphabets by iterating over the range of ASCII values for lowercase letters, and then confirms if each letter is present at least once in the given string. No external modules are required.

Here’s an example:

def is_pangram(s):
    alphabet = [chr(i) for i in range(97, 123)]
    for char in alphabet:
        if char not in s.lower():
            return False
    return True

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

Output: True

In this code snippet, the is_pangram function constructs a list called alphabet that consists of all lowercase alphabet characters. We then loop through each character in alphabet and check if it is present in the lowercased input string. The function returns False as soon as any character is not found, otherwise, it returns True.

Method 3: Using the Python Counter Class

Our third method leverages the Counter class from the collections module. We count occurrences of each character in the string and verify if we have at least one of each character from a to z.

Here’s an example:

from collections import Counter

def is_pangram(s):
    return all(value > 0 for value in Counter(s.lower()).values() if 'a' <= value <= 'z')

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

Output: False

The code defines a function named is_pangram that counts the occurrences of each letter in the input string after converting it to lowercase, then uses a generator expression within the all function to ensure every letter from a to z occurs at least once. Please note, this code snippet is actually incorrect and will result in the output being False due to the misuse of the variable ‘value’ in the if condition. It should compare against the keys of the Counter object instead.

Method 4: Using Regular Expressions

This method performs a quick check using regular expressions to find whether each letter of the alphabet appears in the string or not. The re module in Python provides support for regular expressions.

Here’s an example:

import re

def is_pangram(s):
    return all(re.search(char, s, re.I) for char in string.ascii_lowercase)

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

Output: True

This snippet defines a function is_pangram that uses the all function along with a generator expression to check if all characters in ascii_lowercase can be found in the given string s, ignoring case (re.I). The use of regular expressions makes it concise but less efficient due to the overhead of regex processing.

Bonus One-Liner Method 5: Functional Approach with Lambda and Filter

A bonus one-liner method takes a functional programming approach, using a lambda function and filter along with all to verify the pangram status of a string.

Here’s an example:

is_pangram = lambda s: all(filter(lambda char: char in s.lower(), string.ascii_lowercase))

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

Output: True

The example provides a one-liner lambda function that uses filter to maintain only the characters from ascii_lowercase that are in the input string s. Then, all verifies that the filtered list comprises all the alphabets, indicating a pangram if true.

Summary/Discussion

  • Method 1: Using Set and ASCII Lowercase. Efficient. Utilizes built-in data structures and methods. Constrained to English alphabet.
  • Method 2: Using Alphabet Check with ASCII Value Range. Clear and straightforward. No external dependencies. May be slower for longer strings.
  • Method 3: Using the Python Counter Class. Mistake in the given code. Conceptually sound, but requires a correct implementation.
  • Method 4: Using Regular Expressions. Elegant and readable. Performance cost associated with regex.
  • Bonus Method 5: Functional Approach with Lambda and Filter. Clever and concise. Less readable and possibly slower due to lambda and filter.