`ENCODINGS_LOOKUP` mixes string and bytes keys in the same dict

[sumanjeet0012]

ENCODINGS_LOOKUP is a single dict that uses both str keys (encoding names like "base16") and bytes keys (prefix codes like b"f"). This is confusing, type-unsafe, and could cause subtle bugs if a name happens to match a prefix byte.

Problem

In multibase/multibase.py:

ENCODINGS_LOOKUP = {}
for codec in ENCODINGS:
    ENCODINGS_LOOKUP[codec.encoding] = codec  # str key: "base16"
    ENCODINGS_LOOKUP[codec.code] = codec      # bytes key: b"f"

The resulting dict has mixed key types:

ENCODINGS_LOOKUP = {
    "identity": Encoding(...),     # str
    b"\x00": Encoding(...),        # bytes
    "base2": Encoding(...),        # str
    b"0": Encoding(...),           # bytes
    "base16": Encoding(...),       # str
    b"f": Encoding(...),           # bytes
    # ...
}

Problems:

1. Type confusion — Functions like is_encoding_supported() accept str but the dict also has bytes keys, so is_encoding_supported(b"f") returns True even though the docstring says it takes a str
2. Potential collision — If an encoding name were a single character that matches another encoding's prefix byte, there would be a collision (currently safe but fragile)
3. get_codec() relies on this — It checks data[:4] for emoji, then data[:1] for single-byte prefixes, both against the same mixed dict

Proposed Solution

Split into two separate dicts:

_ENCODINGS_BY_NAME: dict[str, Encoding] = {}
_ENCODINGS_BY_CODE: dict[bytes, Encoding] = {}

for codec in ENCODINGS:
    _ENCODINGS_BY_NAME[codec.encoding] = codec
    _ENCODINGS_BY_CODE[codec.code] = codec

Update all functions to use the appropriate dict:

def is_encoding_supported(encoding: str) -> bool:
    return encoding in _ENCODINGS_BY_NAME

def get_codec(data):
    data = ensure_bytes(data, "utf8")
    # Check emoji first (4-byte prefix)
    if len(data) >= 4 and data[:4] in _ENCODINGS_BY_CODE:
        return _ENCODINGS_BY_CODE[data[:4]]
    # Check single-byte prefix
    if data[:1] in _ENCODINGS_BY_CODE:
        return _ENCODINGS_BY_CODE[data[:1]]
    raise InvalidMultibaseStringError(...)

Keep ENCODINGS_LOOKUP as a backward-compatible alias if needed:

# Backward compatibility
ENCODINGS_LOOKUP = {**_ENCODINGS_BY_NAME, **_ENCODINGS_BY_CODE}

Related

• File: multibase/multibase.py