TheAlgorithms/Python · error · ValueError

Each message character has to be included in alphabet!

Error message

Each message character has to be included in alphabet!

What it means

Raised by trifid_cipher's __prepare helper when any character of the (space-stripped, uppercased) message is not present in the supplied alphabet. The trifid cipher can only encode symbols that exist in its 27-character alphabet, so foreign characters make the number-substitution step impossible.

Source

Thrown at ciphers/trifid_cipher.py:113

        ...
    ValueError: Each message character has to be included in alphabet!

    Testing with numbers

    >>> __prepare(500,'abCdeFghijkLmnopqrStuVwxYZ+')
    Traceback (most recent call last):
        ...
    AttributeError: 'int' object has no attribute 'replace'
    """
    # Validate message and alphabet, set to upper and remove spaces
    alphabet = alphabet.replace(" ", "").upper()
    message = message.replace(" ", "").upper()

    # Check length and characters
    if len(alphabet) != 27:
        raise KeyError("Length of alphabet has to be 27.")
    if any(char not in alphabet for char in message):
        raise ValueError("Each message character has to be included in alphabet!")

    # Generate dictionares
    character_to_number = dict(zip(alphabet, TEST_CHARACTER_TO_NUMBER.values()))
    number_to_character = {
        number: letter for letter, number in character_to_number.items()
    }

    return message, alphabet, character_to_number, number_to_character


def encrypt_message(
    message: str, alphabet: str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ.", period: int = 5
) -> str:
    """
    encrypt_message
    ===============

    Encrypts a message using the trifid_cipher. Any punctuatuion chars that

View on GitHub (pinned to f5988cc097)

Solutions

1. Sanitize the message to A-Z plus '.' before calling: re.sub(r'[^A-Z.]', '', message.upper())
2. Or extend the alphabet with the missing characters while keeping its length at 27
3. Check the error occurs after the length check, so fix any alphabet-length error (error 80) first

Example fix

# before
encrypt_message('ROOM 12', 'ABCDEFGHIJKLMNOPQRSTUVWXYZ.')
# ValueError: Each message character has to be included in alphabet!

# after
import re
encrypt_message(re.sub(r'[^A-Z.]', '', 'ROOM 12'), 'ABCDEFGHIJKLMNOPQRSTUVWXYZ.')

import re
clean = re.sub(r'[^A-Z.]', '', message.upper())
# then pass `clean` and a 27-char alphabet covering it

def message_in_alphabet(message: str, alphabet: str) -> bool:
    a = set(alphabet.replace(' ', '').upper())
    return all(ch in a for ch in message.replace(' ', '').upper())

try:
    encrypt_message(msg, alphabet)
except ValueError as e:
    if 'included in alphabet' in str(e):
        msg = ''.join(c for c in msg.upper() if c in alphabet)
        return encrypt_message(msg, alphabet)
    raise

When it happens

Trigger: Message containing digits or punctuation not in the alphabet: encrypt_message('MEET AT 9PM') (the '9' is not in the default alphabet), or a custom alphabet that omits letters used in the message, e.g. alphabet='ABCDEFGHIJKLMNOQRSTUVWXY.Z' with message 'HELP'.

Common situations: Passing user-typed text with digits, commas, or question marks; using a custom alphabet that drops letters the message still uses; forgetting that spaces are removed automatically but other whitespace/punctuation is not.

Related errors

• Length of alphabet has to be 27.
• Non-binary value was passed to the function
• number must be positive
• The value of input must be non-negative
• Input list must contain at least two elements

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/b05a0fdb5f0e6c7b. Report an issue: GitHub.