boto/boto3 · error · ValueError

Unknown keyword argument: {name}

Error message

Unknown keyword argument: {name}

What it means

Raised by ServiceResource.__init__ when a keyword argument is passed that is not in the resource's declared identifier list (meta.identifiers) and is not 'client'. Resource constructors only accept their defined identifiers (e.g. a Bucket accepts 'name', an Object accepts 'bucket' and 'key'); any other kwarg is rejected to fail fast on typos and mismatches.

Source

Thrown at boto3/resources/base.py:116

        # Create a default client if none was passed
        if kwargs.get('client') is not None:
            self.meta.client = kwargs.get('client')
        else:
            self.meta.client = boto3.client(self.meta.service_name)

        # Allow setting identifiers as positional arguments in the order
        # in which they were defined in the ResourceJSON.
        for i, value in enumerate(args):
            setattr(self, f"_{self.meta.identifiers[i]}", value)

        # Allow setting identifiers via keyword arguments. Here we need
        # extra logic to ignore other keyword arguments like ``client``.
        for name, value in kwargs.items():
            if name == 'client':
                continue

            if name not in self.meta.identifiers:
                raise ValueError(f'Unknown keyword argument: {name}')

            setattr(self, f"_{name}", value)

        # Validate that all identifiers have been set.
        for identifier in self.meta.identifiers:
            if getattr(self, identifier) is None:
                raise ValueError(f'Required parameter {identifier} not set')

    def __repr__(self):
        identifiers = [
            f'{identifier}={repr(getattr(self, identifier))}'
            for identifier in self.meta.identifiers
        ]
        return f"{self.__class__.__name__}({', '.join(identifiers)})"

    def __eq__(self, other):
        # Should be instances of the same resource class
        if other.__class__.__name__ != self.__class__.__name__:

View on GitHub (pinned to c7b4afac23)

Solutions

1. Check resource.meta.identifiers for the accepted keyword names.
2. Pass identifiers positionally to avoid name mismatches.
3. Use the parent resource's accessors (e.g. bucket.Object(key='k')) which fill identifiers automatically.

Example fix

# before
bucket = s3.Bucket(bucket_name='mybucket')

# after
bucket = s3.Bucket('mybucket')
# or
bucket = s3.Bucket(name='mybucket')

def safe_resource(resource_cls, **kwargs):
    allowed = set(resource_cls.meta.identifiers) | {'client'}
    bad = set(kwargs) - allowed
    if bad:
        raise ValueError(f'Unknown kwargs for {resource_cls.__name__}: {bad}. Allowed: {allowed}')
    return resource_cls(**kwargs)

def accepted_identifiers(resource_cls) -> set:
    return set(resource_cls.meta.identifiers)

When it happens

Trigger: s3.Bucket(bucket_name='mybucket') — should be s3.Bucket('mybucket') or s3.Bucket(name='mybucket'). Also s3.Object(bucket='b', key='k', extra='x') where 'extra' is not an identifier.

Common situations: Guessing constructor parameter names instead of checking the resource model; passing client-creation kwargs (like region_name) into a resource constructor; version differences where identifier names changed.

Related errors

• Required parameter {identifier} not set
• The following transfer config options are invalid when prefe
• {self.__class__.__name__} has no load method
• {parent.__class__.__name__} has no load method!
• Unsupported source type: {source}

AI-assisted analysis of boto/boto3@c7b4afac23 (2026-08-04). Data as JSON: /data/errors/5a85c85ac0984b28.json. Report an issue: GitHub.