Python/strings/detecting_english_programmatically.py

import os

UPPERLETTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
LETTERS_AND_SPACE = UPPERLETTERS + UPPERLETTERS.lower() + " \t\n"


def load_dictionary() -> dict[str, None]:
    path = os.path.split(os.path.realpath(__file__))
    english_words: dict[str, None] = {}
    with open(path[0] + "/dictionary.txt") as dictionary_file:
        for word in dictionary_file.read().split("\n"):
            english_words[word] = None
    return english_words


ENGLISH_WORDS = load_dictionary()


def get_english_count(message: str) -> float:
    message = message.upper()
    message = remove_non_letters(message)
    possible_words = message.split()

    if possible_words == []:
        return 0.0

    matches = 0
    for word in possible_words:
        if word in ENGLISH_WORDS:
            matches += 1

    return float(matches) / len(possible_words)


def remove_non_letters(message: str) -> str:
    letters_only = []
    for symbol in message:
        if symbol in LETTERS_AND_SPACE:
            letters_only.append(symbol)
    return "".join(letters_only)


def is_english(
    message: str, word_percentage: int = 20, letter_percentage: int = 85
) -> bool:
    """
    >>> is_english('Hello World')
    True
    >>> is_english('llold HorWd')
    False
    """
    words_match = get_english_count(message) * 100 >= word_percentage
    num_letters = len(remove_non_letters(message))
    message_letters_percentage = (float(num_letters) / len(message)) * 100
    letters_match = message_letters_percentage >= letter_percentage
    return words_match and letters_match


if __name__ == "__main__":
    import doctest

    doctest.testmod()