def get_fetch_input(context, caller):
    """Get s3Fetch formatted context.

    Args:
        context (pypyr.context.Context(): Mandatory. Must contain:
            - s3Fetch: dict. mandatory. Must contain:
                - methodArgs
                    - Bucket: string. s3 bucket name.
                    - Key: string. s3 key name.
        caller (string): Mandatory. __name__ of caller.

    Returns:
        Formatted dict under the context['s3Fetch']

    Raises:
       KeyNotInContextError: s3Fetch or s3Fetch.methodArgs missing
       KeyInContextHasNoValueError: s3Fetch doesn't have a value.
    """
    context.assert_key_has_value(key='s3Fetch', caller=caller)
    return context.get_formatted('s3Fetch')