def is_pangram(
    input_str: str = "The quick brown fox jumps over the lazy dog",
) -> bool:
    # Declare frequency as a set to have unique occurrences of letters
    frequency = set()

    # Replace all the whitespace in our sentence
    input_str = input_str.replace(" ", "")
    for alpha in input_str:
        if "a" <= alpha.lower() <= "z":
            frequency.add(alpha.lower())
    return len(frequency) == 26