TheAlgorithms/Python · error · Exception

encode() accepts only letters of the alphabet and spaces

Error message

encode() accepts only letters of the alphabet and spaces

What it means

Raised by baconian_cipher encode() when, after lowercasing, any character is neither a letter nor a space. The Baconian cipher substitutes each letter with a 5-symbol A/B group from encode_dict, so digits and punctuation have no mapping and are rejected with a generic Exception (not ValueError).

Source

Thrown at ciphers/baconian_cipher.py:58

def encode(word: str) -> str:
    """
    Encodes to Baconian cipher

    >>> encode("hello")
    'AABBBAABAAABABAABABAABBAB'
    >>> encode("hello world")
    'AABBBAABAAABABAABABAABBAB BABAAABBABBAAAAABABAAAABB'
    >>> encode("hello world!")
    Traceback (most recent call last):
        ...
    Exception: encode() accepts only letters of the alphabet and spaces
    """
    encoded = ""
    for letter in word.lower():
        if letter.isalpha() or letter == " ":
            encoded += encode_dict[letter]
        else:
            raise Exception("encode() accepts only letters of the alphabet and spaces")
    return encoded


def decode(coded: str) -> str:
    """
    Decodes from Baconian cipher

    >>> decode("AABBBAABAAABABAABABAABBAB BABAAABBABBAAAAABABAAAABB")
    'hello world'
    >>> decode("AABBBAABAAABABAABABAABBAB")
    'hello'
    >>> decode("AABBBAABAAABABAABABAABBAB BABAAABBABBAAAAABABAAAABB!")
    Traceback (most recent call last):
        ...
    Exception: decode() accepts only 'A', 'B' and spaces
    """
    if set(coded) - {"A", "B", " "} != set():
        raise Exception("decode() accepts only 'A', 'B' and spaces")

View on GitHub (pinned to f5988cc097)

Solutions

1. Sanitize first: ''.join(c for c in text.lower() if c.isalpha() or c == ' ') then encode.
2. Or strip to letters only: ''.join(c for c in text if c.isalpha()).
3. Catch Exception (not just ValueError) if you wrap encode() — it raises bare Exception.

Example fix

# before
encode('hello world!')  # Exception: encode() accepts only letters of the alphabet and spaces

# after
encode(''.join(c for c in 'hello world!' if c.isalpha() or c == ' '))

sanitized = ''.join(c for c in text.lower() if c.isalpha() or c == ' ')
if not sanitized:
    raise ValueError('nothing to encode')

def is_baconian_encodable(s: str) -> bool:
    return all(c.isalpha() or c == ' ' for c in s.lower())

try:
    encode(text)
except Exception as e:  # note: bare Exception, not ValueError
    if 'accepts only letters' in str(e):
        encode(''.join(c for c in text.lower() if c.isalpha() or c == ' '))
    else:
        raise

When it happens

Trigger: Calling encode('hello world!') as in the doctest; also digits ('abc123') or any punctuation ('hi, there?'). Spaces are allowed — only a-z and ' ' pass.

Common situations: Encrypting raw sentences with punctuation or numbers, or assuming the function strips non-letters automatically like a1z26-style ciphers elsewhere in the repo.

Related errors

• plain must contain only lowercase letters (a-z)
• plaintext is empty
• key is empty
• ciphertext is empty
• decode() accepts only 'A', 'B' and spaces

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/29e88a269717d21e. Report an issue: GitHub.