boto/boto3 · error · TypeError

Unsupported type "{type(value)}" for value "{value}"

Error message

Unsupported type "{type(value)}" for value "{value}"

What it means

Raised by TypeSerializer._get_dynamodb_type when serialize() receives a Python value that matches none of the supported DynamoDB type checks (None, bool, int/Decimal, str, Binary/bytes/bytearray, sets of those, Mapping, list/tuple). The serializer dispatches on type; an unrecognized type (custom object, datetime, complex, frozenset of unsupported, etc.) cannot be mapped to a DynamoDB type and is rejected.

Source

Thrown at boto3/dynamodb/types.py:153

        elif self._is_type_set(value, self._is_number):
            dynamodb_type = NUMBER_SET

        elif self._is_type_set(value, self._is_string):
            dynamodb_type = STRING_SET

        elif self._is_type_set(value, self._is_binary):
            dynamodb_type = BINARY_SET

        elif self._is_map(value):
            dynamodb_type = MAP

        elif self._is_listlike(value):
            dynamodb_type = LIST

        else:
            msg = f'Unsupported type "{type(value)}" for value "{value}"'
            raise TypeError(msg)

        return dynamodb_type

    def _is_null(self, value):
        if value is None:
            return True
        return False

    def _is_boolean(self, value):
        if isinstance(value, bool):
            return True
        return False

    def _is_number(self, value):
        if isinstance(value, (int, Decimal)):
            return True
        elif isinstance(value, float):
            raise TypeError(

View on GitHub (pinned to c7b4afac23)

Solutions

1. Convert datetime/date to ISO-format strings: dt.isoformat().
2. Convert custom objects to dicts or primitives before putting.
3. Ensure sets are homogeneous (all int/Decimal, all str, or all bytes/Binary).
4. Use Decimal for all numbers instead of float or numeric strings.

Example fix

# before
from datetime import datetime
table.put_item(Item={'ts': datetime.now()})

# after
table.put_item(Item={'ts': datetime.now().isoformat()})

from datetime import date, datetime
from decimal import Decimal

def normalize_for_dynamodb(value):
    if isinstance(value, (datetime, date)):
        return value.isoformat()
    if isinstance(value, float):
        return Decimal(str(value))
    if hasattr(value, '__dict__') and not isinstance(value, (str, bytes, bytearray)):
        return {k: normalize_for_dynamodb(v) for k, v in vars(value).items()}
    return value

def normalize_item(item):
    return {k: normalize_for_dynamodb(v) for k, v in item.items()}

from decimal import Decimal
from boto3.dynamodb.types import Binary

def is_dynamodb_supported(v) -> bool:
    return isinstance(v, (type(None), bool, int, Decimal, str, bytes, bytearray, Binary, list, tuple, dict, set))

try:
    table.put_item(Item=item)
except TypeError as e:
    if 'Unsupported type' in str(e):
        item = normalize_item(item)
        table.put_item(Item=item)
    else:
        raise

When it happens

Trigger: table.put_item(Item={'when': datetime.now()}) — datetime is unsupported. Also serialize(complex(1,2)), serialize(object()), or a set containing mixed/unsupported types. Note: float is caught separately (see error 10), and frozenset of unsupported inner types falls through here.

Common situations: Storing datetime/date objects without conversion to ISO strings; storing custom dataclass/pydantic objects without dict conversion; sets mixing types that fail every _is_type_set check.

Related errors

• Value must be of the following types: {types}
• Float types are not supported. Use Decimal types instead.
• Infinity and NaN not supported
• Value must be a nonempty dictionary whose key is a valid dyn
• Dynamodb type {dynamodb_type} is not supported

AI-assisted analysis of boto/boto3@c7b4afac23 (2026-08-04). Data as JSON: /data/errors/fdadafabeb86747f.json. Report an issue: GitHub.