7.2 结构化输出解析与校验

模型输出需要被转换为类型安全的结构化形式才能可靠地驱动后续操作。本节介绍 Claude 的消息类型系统、非流式与流式响应的解析方法、Pydantic 参数验证以及完整的解析管道设计。

7.2.1 核心问题

原始 API 响应是无类型的字符串或弱类型的 JSON。要将其安全地转换为类型安全的结构化表示，需要解决：

1. 类型识别：区分文本、工具调用、思考块等不同内容类型

2. 增量解析：处理流式响应的片段化更新

3. 结构校验：验证解析结果的完整性与合法性

4. 向后兼容：支持不同 API 版本和模型的差异

7.2.2 Claude 的消息类型系统

Claude API 返回的消息(Message)由多个内容块(ContentBlock)组成，每个块有不同的类型：

from dataclasses import dataclass
from enum import Enum
from typing import Optional, List, Any

class ContentBlockType(Enum):
    TEXT = "text"
    TOOL_USE = "tool_use"
    THINKING = "thinking"

@dataclass
class TextBlock:
    """文本内容块"""
    type: str = "text"
    text: str = ""

@dataclass
class ToolUseBlock:
    """工具调用块"""
    type: str = "tool_use"
    id: str = ""
    name: str = ""
    input: dict = None  # JSON 输入参数

@dataclass
class ThinkingBlock:
    """思考过程块(Adaptive Thinking)"""
    type: str = "thinking"
    thinking: str = ""

ContentBlock = TextBlock | ToolUseBlock | ThinkingBlock

@dataclass
class ParsedMessage:
    """解析后的完整消息"""
    content_blocks: List[ContentBlock]
    stop_reason: str  # "end_turn", "tool_use", "max_tokens"
    tokens_used: int

    def text_content(self) -> str:
        """提取所有文本内容"""
        texts = [
            block.text for block in self.content_blocks
            if isinstance(block, TextBlock)
        ]
        return "".join(texts)

    def tool_calls(self) -> List[ToolUseBlock]:
        """提取所有工具调用"""
        return [
            block for block in self.content_blocks
            if isinstance(block, ToolUseBlock)
        ]

    def thinking_content(self) -> Optional[str]:
        """提取思考过程"""
        for block in self.content_blocks:
            if isinstance(block, ThinkingBlock):
                return block.thinking
        return None

非流式解析

完整响应的解析实现方式如下：

import json
from typing import Dict, Any

class ResponseParser:
    """API 响应解析器"""

    @staticmethod
    def parse_response(raw_response: Dict[str, Any]) -> ParsedMessage:
        """解析完整的 API 响应"""
        content_blocks = []

        # 遍历响应的 content 数组
        for block in raw_response.get("content", []):
            block_type = block.get("type")

            if block_type == "text":
                content_blocks.append(TextBlock(
                    type="text",
                    text=block.get("text", "")
                ))

            elif block_type == "tool_use":
                # 工具调用:需要解析 JSON 输入
                input_data = block.get("input", {})
                if isinstance(input_data, str):
                    try:
                        input_data = json.loads(input_data)
                    except json.JSONDecodeError as e:
                        # 捕获 JSON 解析失败,记录错误并使用空对象
                        print(f"警告: JSON 解析失败: {e}, 使用空参数")
                        input_data = {}

                content_blocks.append(ToolUseBlock(
                    type="tool_use",
                    id=block.get("id", ""),
                    name=block.get("name", ""),
                    input=input_data
                ))

            elif block_type == "thinking":
                content_blocks.append(ThinkingBlock(
                    type="thinking",
                    thinking=block.get("thinking", "")
                ))

        return ParsedMessage(
            content_blocks=content_blocks,
            stop_reason=raw_response.get("stop_reason", "end_turn"),
            tokens_used=(
                raw_response.get("usage", {}).get("input_tokens", 0) +
                raw_response.get("usage", {}).get("output_tokens", 0)
            )
        )

流式解析

流式响应分块到达，需要增量构建完整消息。关键是跟踪当前正在构建的块状态：

import json
from enum import Enum
from typing import Dict, Any, Optional

class StreamEventType(Enum):
    MESSAGE_START = "message_start"
    CONTENT_BLOCK_START = "content_block_start"
    CONTENT_BLOCK_DELTA = "content_block_delta"
    CONTENT_BLOCK_STOP = "content_block_stop"
    MESSAGE_DELTA = "message_delta"
    MESSAGE_STOP = "message_stop"

class StreamingParser:
    """流式响应解析器"""

    def __init__(self):
        self.content_blocks = []
        self.current_block = None
        self.block_index = 0
        self.stop_reason = "end_turn"
        self.tokens_used = 0
        self.partial_json_buffer = ""  # 累积工具参数的 JSON 分片

    def process_event(self, event: Dict[str, Any]) -> Optional[ParsedMessage]:
        """处理单个流式事件"""
        event_type = event.get("type")

        if event_type == "message_start":
            # 消息开始,重置状态
            self.content_blocks = []
            self.current_block = None
            self.block_index = 0
            usage = event.get("message", {}).get("usage", {})
            self.tokens_used = (
                usage.get("input_tokens", 0)
                + usage.get("cache_creation_input_tokens", 0)
                + usage.get("cache_read_input_tokens", 0)
            )

        elif event_type == "content_block_start":
            # 新块开始
            self.block_index = event.get("index", 0)
            block_info = event.get("content_block", {})
            block_type = block_info.get("type")

            if block_type == "text":
                self.current_block = TextBlock(type="text", text="")
            elif block_type == "tool_use":
                self.current_block = ToolUseBlock(
                    type="tool_use",
                    id=block_info.get("id", ""),
                    name=block_info.get("name", ""),
                    input={}
                )
                self.partial_json_buffer = ""  # 参数 JSON 跨多个 delta 到达,需累积
            elif block_type == "thinking":
                self.current_block = ThinkingBlock(type="thinking", thinking="")

            # 确保数组足够长
            while len(self.content_blocks) <= self.block_index:
                self.content_blocks.append(None)

        elif event_type == "content_block_delta":
            # 块内容增量更新
            delta = event.get("delta", {})
            delta_type = delta.get("type")

            if delta_type == "text_delta":
                if isinstance(self.current_block, TextBlock):
                    self.current_block.text += delta.get("text", "")

            elif delta_type == "input_json_delta":
                # 工具调用的 JSON 增量:单个分片(如 '{"query": "Py')通常不是
                # 合法 JSON,只能累积,待 content_block_stop 时一次性解析
                if isinstance(self.current_block, ToolUseBlock):
                    self.partial_json_buffer += delta.get("partial_json", "")

            elif delta_type == "thinking_delta":
                if isinstance(self.current_block, ThinkingBlock):
                    self.current_block.thinking += delta.get("thinking", "")

        elif event_type == "content_block_stop":
            # 块完成:工具块在此刻才拥有完整的参数 JSON
            if isinstance(self.current_block, ToolUseBlock) and self.partial_json_buffer:
                try:
                    self.current_block.input = json.loads(self.partial_json_buffer)
                except json.JSONDecodeError:
                    self.current_block.input = {}
                self.partial_json_buffer = ""
            # 保存到数组
            if self.current_block is not None:
                self.content_blocks[self.block_index] = self.current_block
                self.current_block = None

        elif event_type == "message_delta":
            # 消息完成
            delta = event.get("delta", {})
            self.stop_reason = delta.get("stop_reason", "end_turn")
            usage = event.get("usage", {})
            self.tokens_used += usage.get("output_tokens", 0)

            # 返回完整的解析结果
            return ParsedMessage(
                content_blocks=[b for b in self.content_blocks if b],
                stop_reason=self.stop_reason,
                tokens_used=self.tokens_used
            )

        return None  # 消息未完成

使用流式解析器

流式解析器的具体使用方式如下：

import json

class StreamIterator:
    """流式迭代器,隐藏解析复杂性"""

    def __init__(self, api_stream):
        self.api_stream = api_stream
        self.parser = StreamingParser()

    def __iter__(self):
        for event_data in self.api_stream:
            try:
                event = json.loads(event_data)
            except json.JSONDecodeError as e:
                # JSON 解析失败,记录错误并跳过该事件
                print(f"警告: 流式事件 JSON 解析失败: {e}, 跳过该事件")
                continue
            result = self.parser.process_event(event)
            if result is not None:
                yield result

# 使用示例:api_stream 应是“逐条 JSON 字符串”的原始事件流(如 SSE 的 data: 行)。
# 注意:anthropic SDK 的 client.messages.stream() 产出的是已解析的事件对象,
# 直接遍历即可,不应再传入本迭代器做 json.loads。
for parsed_message in StreamIterator(raw_sse_data_lines):
    print(f"接收到消息: {parsed_message.text_content()}")
    for tool_call in parsed_message.tool_calls():
        print(f"  工具调用: {tool_call.name}({tool_call.input})")

Pydantic 校验

使用 Pydantic 定义预期的工具参数结构，并在解析后进行验证：

from pydantic import BaseModel, ValidationError, field_validator
from typing import Optional

class SearchToolInput(BaseModel):
    """搜索工具的输入参数"""
    query: str
    max_results: int = 10
    language: str = "en"

    @field_validator("max_results")
    @classmethod
    def validate_max_results(cls, v):
        if v < 1 or v > 100:
            raise ValueError("max_results 必须在 1-100 之间")
        return v

class ToolCallValidator:
    """工具调用参数验证"""

    TOOL_SCHEMAS = {
        "search": SearchToolInput,
        "database_query": "DatabaseQueryInput",
        # ... 其他工具
    }

    @staticmethod
    def validate_tool_call(tool_call: ToolUseBlock) -> bool:
        """验证工具调用的合法性"""
        tool_name = tool_call.name
        if tool_name not in ToolCallValidator.TOOL_SCHEMAS:
            raise ValueError(f"未知的工具: {tool_name}")

        schema = ToolCallValidator.TOOL_SCHEMAS[tool_name]
        try:
            schema(**tool_call.input)
            return True
        except ValidationError as e:
            # 捕获 Pydantic 验证错误,提供详细错误信息
            error_msg = "; ".join([f"{err['loc']}: {err['msg']}" for err in e.errors()])
            raise ValueError(f"工具参数验证失败: {error_msg}")
        except (TypeError, AttributeError) as e:
            # 捕获参数类型错误
            raise ValueError(f"工具调用格式错误: {e}")

# 使用
tool_call = ToolUseBlock(
    id="call_123",
    name="search",
    input={"query": "Python async", "max_results": 10}
)
try:
    if ToolCallValidator.validate_tool_call(tool_call):
        print("工具调用有效")
except ValueError as e:
    print(f"验证失败: {e}")

解析管道

完整的解析管道实现如下：

class ParsingPipeline:
    """完整的解析管道"""

    def __init__(self):
        self.parser = ResponseParser()
        self.validator = ToolCallValidator()

    def parse_and_validate(
        self, raw_response: Dict[str, Any]
    ) -> ParsedMessage:
        """解析并验证响应"""
        # 步骤 1:解析
        parsed = self.parser.parse_response(raw_response)

        # 步骤 2:验证工具调用
        for tool_call in parsed.tool_calls():
            self.validator.validate_tool_call(tool_call)

        # 步骤 3:检查完整性
        if parsed.stop_reason == "max_tokens":
            raise ValueError("响应因 token 限制被截断")

        return parsed

输出解析管道架构

结构化输出的解析流程如下所示：

图 7-2：输出解析管道 —— 从原始响应逐步转换为类型安全的结构化数据

总结

结构化输出解析通过：

• 类型系统 (TextBlock/ToolUseBlock/ThinkingBlock)提供类型安全

• 非流式与流式双路径 支持不同使用场景

• 增量解析 实现高效的流式处理

• Pydantic 校验 确保参数合法性

这是构建可靠智能体的基础，为下一步的质量门控做准备。