boto/boto3 · error · ValueError

Required parameter {identifier} not set

Error message

Required parameter {identifier} not set

What it means

Raised by ServiceResource.__init__ during the final validation loop: after processing all positional and keyword arguments, it checks every identifier in meta.identifiers; if any is still None, the resource cannot address a specific AWS entity and construction is aborted. This catches incomplete resource instantiation.

Source

Thrown at boto3/resources/base.py:123

        # 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__:
            return False

        # Each of the identifiers should have the same value in both
        # instances, e.g. two buckets need the same name to be equal.
        for identifier in self.meta.identifiers:
            if getattr(self, identifier) != getattr(other, identifier):
                return False

View on GitHub (pinned to c7b4afac23)

Solutions

1. Supply every required identifier: s3.Object(bucket_name='b', key='k').
2. Use parent-resource accessors (bucket.Object(key='k')) which inject the parent identifier automatically.
3. Check resource.meta.identifiers and ensure none is None before or after construction.

Example fix

# before
obj = s3.Object(key='k')  # missing bucket

# after
obj = s3.Object(bucket_name='mybucket', key='k')
# or via parent
obj = s3.Bucket('mybucket').Object('k')

def build_resource(resource_cls, **kwargs):
    missing = [i for i in resource_cls.meta.identifiers if kwargs.get(i) is None]
    if missing:
        raise ValueError(f'Missing required identifiers: {missing}')
    return resource_cls(**kwargs)

def all_identifiers_set(resource) -> bool:
    return all(getattr(resource, i) is not None for i in resource.meta.identifiers)

When it happens

Trigger: s3.Object(key='k') — missing 'bucket' identifier. Also constructing a resource with fewer positional args than required identifiers, or passing an identifier as None explicitly.

Common situations: Building a child resource without supplying the parent identifier; optional fields mistaken for identifiers; programmatic resource creation where a loop omits one field.

Related errors

• Unknown keyword argument: {name}
• {self.__class__.__name__} has no load method
• {parent.__class__.__name__} has no load method!
• Unsupported source type: {source}
• Unsupported source type: {source}

AI-assisted analysis of boto/boto3@c7b4afac23 (2026-08-04). Data as JSON: /data/errors/6563e5fcf9a924a0.json. Report an issue: GitHub.