【超丝滑的LangChain教程】LangChain进阶之Agents_langchain agent

01 Agent介绍

在LangChain中，Agent 是一个核心概念，它代表了一种能够利用语言模型（LLM）和其他工具来执行复杂任务的系统。Agent的设计目的是为了处理那些简单的语言模型可能无法直接解决的问题，尤其是当这些任务涉及到多个步骤或者需要外部数据源的情况。

• Agent 在LangChain中扮演着一个协调者和决策者的角色，它能够根据给定的任务和目标，决定使用哪些工具以及如何组合这些工具来达到目的。

• Agent会根据输入的指令和上下文信息，调用不同的工具（如搜索引擎、数据库查询、API调用等）来获取所需的信息，并将这些信息整合起来形成最终的响应。

Agent（代理）的核心思想是使用语言模型来选择要执行的一系列操作。

在Chain（链）中，一系列操作被硬编码在代码中。在Agent（代理）中，语言模型用作推理引擎，以确定要执行哪些操作以及按什么顺序执行。

Agent的工作流程

• 输入理解：Agent首先解析用户输入，理解其意图和需求。
• 计划制定：基于对输入的理解，Agent会制定一个执行计划，决定使用哪些工具和执行的顺序。
• 工具调用：Agent按照计划调用相应的工具，执行必要的操作。
• 结果整合：收集所有工具返回的结果，进行整合和解析，形成最终的输出。
• 反馈循环：如果任务没有完成或者需要进一步的信息，Agent可以迭代上述过程直到满足条件为止。

Agent的组成部分

• Tools：Agent可以访问的工具集，每个工具通常执行一个特定的功能。
• Executor：执行Agent计划的逻辑。
• Prompt Templates：指导Agent如何理解和处理输入的模板，可以定制化以适应不同任务。

创建Agent的步骤

• 定义工具：选择或创建适合任务的工具。
• 初始化执行器：设置执行器，这通常涉及选择一个语言模型。
• 设置提示词：编写或选择适当的prompt模板，帮助Agent理解任务。
• 配置Agent：将工具、执行器和提示词组合成一个Agent实例。

02 基本使用

我们这里就简单点，问下“美国现任总统是谁？”。

• 首先，确定我们要使用的tool。这里我们使用Wikipedia，这也是LangChain内置的一个tool，用起来比较方便~
• 其次，我们要定义好我们的提示词。一般情况下有两种方式：一种是我们自己定义提示词，告诉模型我们有哪些tool，每个tool的具体使用场景，以及你模型要做些什么（说句心里话，稍微有点复杂）；另一种方式是使用langchainhub内置的一些提示词（说句实在话，好用）。
• 然后我们创建代理Agent。这里一般情况下我们都会使用内置的创建方法，当然，你说你想自己自定义创建Agent行不行？行是肯定行的，但是不建议且没必要！说真的，我都不知道你想骚点啥~
• 最后，我们需要创建AgentExecutor来执行整个agent的逻辑得到最终结果。

具体代码如下：

from langchain_community.agent_toolkits.load_tools import load_tools
from langchain.agents import create_react_agent, AgentExecutor
from langchain import hub

# wikipedia
tools = load_tools(['wikipedia'])
# prompt = hub.pull("hwchase17/react")
prompt = hub.pull("hwchase17/react-chat")
agent = create_react_agent(llm_model, tools, prompt)
agent_executor = AgentExecutor(agent=agent, tools=tools, verbose=True)
agent_executor.invoke({"input":"美国现任总统是谁？","chat_history":[]})

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执行流程日志如下：

[chain/start] [chain:AgentExecutor] Entering Chain run with input:
{
  "input": "美国现任总统是谁？"
}
[chain/start] [chain:AgentExecutor > chain:RunnableSequence] Entering Chain run with input:
{
  "input": ""
}
[chain/start] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad>] Entering Chain run with input:
{
  "input": ""
}
[chain/start] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad> > chain:RunnableParallel<agent_scratchpad>] Entering Chain run with input:
{
  "input": ""
}
[chain/start] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad> > chain:RunnableParallel<agent_scratchpad> > chain:RunnableLambda] Entering Chain run with input:
{
  "input": ""
}
[chain/end] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad> > chain:RunnableParallel<agent_scratchpad> > chain:RunnableLambda] [0ms] Exiting Chain run with output:
{
  "output": ""
}
[chain/end] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad> > chain:RunnableParallel<agent_scratchpad>] [1ms] Exiting Chain run with output:
{
  "agent_scratchpad": ""
}
[chain/end] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad>] [3ms] Exiting Chain run with output:
{
  "input": "美国现任总统是谁？",
  "intermediate_steps": [],
  "agent_scratchpad": ""
}
[chain/start] [chain:AgentExecutor > chain:RunnableSequence > prompt:PromptTemplate] Entering Prompt run with input:
{
  "input": "美国现任总统是谁？",
  "intermediate_steps": [],
  "agent_scratchpad": ""
}
[chain/end] [chain:AgentExecutor > chain:RunnableSequence > prompt:PromptTemplate] [2ms] Exiting Prompt run with output:
[outputs]
[llm/start] [chain:AgentExecutor > chain:RunnableSequence > llm:Tongyi] Entering LLM run with input:
{
  "prompts": [
    "Answer the following questions as best you can. You have access to the following tools:\n\nwikipedia: A wrapper around Wikipedia. Useful for when you need to answer general questions about people, places, companies, facts, historical events, or other subjects. Input should be a search query.\n\nUse the following format:\n\nQuestion: the input question you must answer\nThought: you should always think about what to do\nAction: the action to take, should be one of [wikipedia]\nAction Input: the input to the action\nObservation: the result of the action\n... (this Thought/Action/Action Input/Observation can repeat N times)\nThought: I now know the final answer\nFinal Answer: the final answer to the original input question\n\nBegin!\n\nQuestion: 美国现任总统是谁？\nThought:"
  ]
}
[llm/end] [chain:AgentExecutor > chain:RunnableSequence > llm:Tongyi] [1.60s] Exiting LLM run with output:
{
  "generations": [
    [
      {
        "text": "I need to find out who the current president of the United States is.\nAction: wikipedia\nAction Input: President of the United States\n",
        "generation_info": {
          "finish_reason": "stop",
          "request_id": "33fa1726-1736-98d9-8aef-fa45c1ba0007",
          "token_usage": {
            "input_tokens": 175,
            "output_tokens": 28,
            "total_tokens": 203
          }
        },
        "type": "Generation"
      }
    ]
  ],
  "llm_output": null,
  "run": null
}
[chain/start] [chain:AgentExecutor > chain:RunnableSequence > parser:ReActSingleInputOutputParser] Entering Parser run with input:
{
  "input": "I need to find out who the current president of the United States is.\nAction: wikipedia\nAction Input: President of the United States\n"
}
[chain/end] [chain:AgentExecutor > chain:RunnableSequence > parser:ReActSingleInputOutputParser] [0ms] Exiting Parser run with output:
[outputs]
[chain/end] [chain:AgentExecutor > chain:RunnableSequence] [1.61s] Exiting Chain run with output:
[outputs]
[tool/start] [chain:AgentExecutor > tool:wikipedia] Entering Tool run with input:
"President of the United States"
[tool/end] [chain:AgentExecutor > tool:wikipedia] [11.90s] Exiting Tool run with output:
"Page: President of the United States
Summary: The president of the United States (POTUS) is the head of state/head of government of the United States of America. The president directs the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces.
The power of the presidency has grown substantially since the first president, George Washington, took office in 1789. While presidential power has ebbed and flowed over time, the presidency has played an increasingly significant role in American political life since the beginning of the 20th century, carrying over into the 21st century with notable expansions during the presidencies of Franklin D. Roosevelt and George W. Bush. In modern times, the president is one of the world's most powerful political figures and the leader of the world's only remaining superpower. As the leader of the nation with the largest economy by nominal GDP, the president possesses significant domestic and international hard and soft power. For much of the 20th century, especially during the Cold War, the U.S. president was often called "the leader of the free world".
Article II of the Constitution establishes the executive branch of the federal government and vests executive power in the president. The power includes the execution and enforcement of federal law and the responsibility to appoint federal executive, diplomatic, regulatory, and judicial officers.  Based on constitutional provisions empowering the president to appoint and receive ambassadors and conclude treaties with foreign powers, and on subsequent laws enacted by Congress, the modern presidency has primary responsibility for conducting U.S. foreign policy. The role includes responsibility for directing the world's most expensive military, which has the second-largest nuclear arsenal.
The president also plays a leading role in federal legislation and domestic policymaking. As part of the system of separation of powers, Article I, Section 7 of the Constitution gives the president the power to sign or veto federal legislation. Since modern presidents are typically viewed as leaders of their political parties, major policymaking is significantly shaped by the outcome of presidential elections, with presidents taking an active role in promoting their policy priorities to members of Congress who are often electorally dependent on the president. In recent decades, presidents have also made increasing use of executive orders, agency regulations, and judicial appointments to shape domestic policy.
The president is elected indirectly through the Electoral College to a four-year term, along with the vice president. Under the Twenty-second Amendment, ratified in 1951, no person who has been elected to two presidential terms may be elected to a third. In addition, nine vice presidents have become president by virtue of a president's intra-term death or resignation. In all, 45 individuals have served 46 presidencies spanning 58 four-year terms. Joe Biden is the 46th and current president, having assumed office on January 20, 2021.

Page: List of presidents of the United States
Summary: The president of the United States is the head of state and head of government of the United States, indirectly elected to a four-year term via the Electoral College. The officeholder leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces. Since the office was established in 1789, 45 men have served in 46 presidencies. The first president, George Washington, won a unanimous vote of the Electoral College. Grover Cleveland served two non-consecutive terms and is therefore counted as the 22nd and 24th president of the United States, giving rise to the discrepancy between the number of presidencies and the number of individuals who have served as president.
The presidency of William Henry Harrison, who died 31 days after taking office in 1841, was the shortest in Ameri"
[chain/start] [chain:AgentExecutor > chain:RunnableSequence] Entering Chain run with input:
{
  "input": ""
}
[chain/start] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad>] Entering Chain run with input:
{
  "input": ""
}
[chain/start] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad> > chain:RunnableParallel<agent_scratchpad>] Entering Chain run with input:
{
  "input": ""
}
[chain/start] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad> > chain:RunnableParallel<agent_scratchpad> > chain:RunnableLambda] Entering Chain run with input:
{
  "input": ""
}
[chain/end] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad> > chain:RunnableParallel<agent_scratchpad> > chain:RunnableLambda] [0ms] Exiting Chain run with output:
{
  "output": "I need to find out who the current president of the United States is.\nAction: wikipedia\nAction Input: President of the United States\n\nObservation: Page: President of the United States\nSummary: The president of the United States (POTUS) is the head of state/head of government of the United States of America. The president directs the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces.\nThe power of the presidency has grown substantially since the first president, George Washington, took office in 1789. While presidential power has ebbed and flowed over time, the presidency has played an increasingly significant role in American political life since the beginning of the 20th century, carrying over into the 21st century with notable expansions during the presidencies of Franklin D. Roosevelt and George W. Bush. In modern times, the president is one of the world's most powerful political figures and the leader of the world's only remaining superpower. As the leader of the nation with the largest economy by nominal GDP, the president possesses significant domestic and international hard and soft power. For much of the 20th century, especially during the Cold War, the U.S. president was often called "the leader of the free world".\nArticle II of the Constitution establishes the executive branch of the federal government and vests executive power in the president. The power includes the execution and enforcement of federal law and the responsibility to appoint federal executive, diplomatic, regulatory, and judicial officers.  Based on constitutional provisions empowering the president to appoint and receive ambassadors and conclude treaties with foreign powers, and on subsequent laws enacted by Congress, the modern presidency has primary responsibility for conducting U.S. foreign policy. The role includes responsibility for directing the world's most expensive military, which has the second-largest nuclear arsenal.\nThe president also plays a leading role in federal legislation and domestic policymaking. As part of the system of separation of powers, Article I, Section 7 of the Constitution gives the president the power to sign or veto federal legislation. Since modern presidents are typically viewed as leaders of their political parties, major policymaking is significantly shaped by the outcome of presidential elections, with presidents taking an active role in promoting their policy priorities to members of Congress who are often electorally dependent on the president. In recent decades, presidents have also made increasing use of executive orders, agency regulations, and judicial appointments to shape domestic policy.\nThe president is elected indirectly through the Electoral College to a four-year term, along with the vice president. Under the Twenty-second Amendment, ratified in 1951, no person who has been elected to two presidential terms may be elected to a third. In addition, nine vice presidents have become president by virtue of a president's intra-term death or resignation. In all, 45 individuals have served 46 presidencies spanning 58 four-year terms. Joe Biden is the 46th and current president, having assumed office on January 20, 2021.\n\nPage: List of presidents of the United States\nSummary: The president of the United States is the head of state and head of government of the United States, indirectly elected to a four-year term via the Electoral College. The officeholder leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces. Since the office was established in 1789, 45 men have served in 46 presidencies. The first president, George Washington, won a unanimous vote of the Electoral College. Grover Cleveland served two non-consecutive terms and is therefore counted as the 22nd and 24th president of the United States, giving rise to the discrepancy between the number of presidencies and the number of individuals who have served as president.\nThe presidency of William Henry Harrison, who died 31 days after taking office in 1841, was the shortest in Ameri\nThought: "
}
[chain/end] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad> > chain:RunnableParallel<agent_scratchpad>] [2ms] Exiting Chain run with output:
{
  "agent_scratchpad": "I need to find out who the current president of the United States is.\nAction: wikipedia\nAction Input: President of the United States\n\nObservation: Page: President of the United States\nSummary: The president of the United States (POTUS) is the head of state/head of government of the United States of America. The president directs the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces.\nThe power of the presidency has grown substantially since the first president, George Washington, took office in 1789. While presidential power has ebbed and flowed over time, the presidency has played an increasingly significant role in American political life since the beginning of the 20th century, carrying over into the 21st century with notable expansions during the presidencies of Franklin D. Roosevelt and George W. Bush. In modern times, the president is one of the world's most powerful political figures and the leader of the world's only remaining superpower. As the leader of the nation with the largest economy by nominal GDP, the president possesses significant domestic and international hard and soft power. For much of the 20th century, especially during the Cold War, the U.S. president was often called "the leader of the free world".\nArticle II of the Constitution establishes the executive branch of the federal government and vests executive power in the president. The power includes the execution and enforcement of federal law and the responsibility to appoint federal executive, diplomatic, regulatory, and judicial officers.  Based on constitutional provisions empowering the president to appoint and receive ambassadors and conclude treaties with foreign powers, and on subsequent laws enacted by Congress, the modern presidency has primary responsibility for conducting U.S. foreign policy. The role includes responsibility for directing the world's most expensive military, which has the second-largest nuclear arsenal.\nThe president also plays a leading role in federal legislation and domestic policymaking. As part of the system of separation of powers, Article I, Section 7 of the Constitution gives the president the power to sign or veto federal legislation. Since modern presidents are typically viewed as leaders of their political parties, major policymaking is significantly shaped by the outcome of presidential elections, with presidents taking an active role in promoting their policy priorities to members of Congress who are often electorally dependent on the president. In recent decades, presidents have also made increasing use of executive orders, agency regulations, and judicial appointments to shape domestic policy.\nThe president is elected indirectly through the Electoral College to a four-year term, along with the vice president. Under the Twenty-second Amendment, ratified in 1951, no person who has been elected to two presidential terms may be elected to a third. In addition, nine vice presidents have become president by virtue of a president's intra-term death or resignation. In all, 45 individuals have served 46 presidencies spanning 58 four-year terms. Joe Biden is the 46th and current president, having assumed office on January 20, 2021.\n\nPage: List of presidents of the United States\nSummary: The president of the United States is the head of state and head of government of the United States, indirectly elected to a four-year term via the Electoral College. The officeholder leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces. Since the office was established in 1789, 45 men have served in 46 presidencies. The first president, George Washington, won a unanimous vote of the Electoral College. Grover Cleveland served two non-consecutive terms and is therefore counted as the 22nd and 24th president of the United States, giving rise to the discrepancy between the number of presidencies and the number of individuals who have served as president.\nThe presidency of William Henry Harrison, who died 31 days after taking office in 1841, was the shortest in Ameri\nThought: "
}
[chain/end] [chain:AgentExecutor > chain:RunnableSequence > chain:RunnableAssign<agent_scratchpad>] [5ms] Exiting Chain run with output:
[outputs]
[chain/start] [chain:AgentExecutor > chain:RunnableSequence > prompt:PromptTemplate] Entering Prompt run with input:
[inputs]
[chain/end] [chain:AgentExecutor > chain:RunnableSequence > prompt:PromptTemplate] [0ms] Exiting Prompt run with output:
[outputs]
[llm/start] [chain:AgentExecutor > chain:RunnableSequence > llm:Tongyi] Entering LLM run with input:
{
  "prompts": [
    "Answer the following questions as best you can. You have access to the following tools:\n\nwikipedia: A wrapper around Wikipedia. Useful for when you need to answer general questions about people, places, companies, facts, historical events, or other subjects. Input should be a search query.\n\nUse the following format:\n\nQuestion: the input question you must answer\nThought: you should always think about what to do\nAction: the action to take, should be one of [wikipedia]\nAction Input: the input to the action\nObservation: the result of the action\n... (this Thought/Action/Action Input/Observation can repeat N times)\nThought: I now know the final answer\nFinal Answer: the final answer to the original input question\n\nBegin!\n\nQuestion: 美国现任总统是谁？\nThought:I need to find out who the current president of the United States is.\nAction: wikipedia\nAction Input: President of the United States\n\nObservation: Page: President of the United States\nSummary: The president of the United States (POTUS) is the head of state/head of government of the United States of America. The president directs the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces.\nThe power of the presidency has grown substantially since the first president, George Washington, took office in 1789. While presidential power has ebbed and flowed over time, the presidency has played an increasingly significant role in American political life since the beginning of the 20th century, carrying over into the 21st century with notable expansions during the presidencies of Franklin D. Roosevelt and George W. Bush. In modern times, the president is one of the world's most powerful political figures and the leader of the world's only remaining superpower. As the leader of the nation with the largest economy by nominal GDP, the president possesses significant domestic and international hard and soft power. For much of the 20th century, especially during the Cold War, the U.S. president was often called "the leader of the free world".\nArticle II of the Constitution establishes the executive branch of the federal government and vests executive power in the president. The power includes the execution and enforcement of federal law and the responsibility to appoint federal executive, diplomatic, regulatory, and judicial officers.  Based on constitutional provisions empowering the president to appoint and receive ambassadors and conclude treaties with foreign powers, and on subsequent laws enacted by Congress, the modern presidency has primary responsibility for conducting U.S. foreign policy. The role includes responsibility for directing the world's most expensive military, which has the second-largest nuclear arsenal.\nThe president also plays a leading role in federal legislation and domestic policymaking. As part of the system of separation of powers, Article I, Section 7 of the Constitution gives the president the power to sign or veto federal legislation. Since modern presidents are typically viewed as leaders of their political parties, major policymaking is significantly shaped by the outcome of presidential elections, with presidents taking an active role in promoting their policy priorities to members of Congress who are often electorally dependent on the president. In recent decades, presidents have also made increasing use of executive orders, agency regulations, and judicial appointments to shape domestic policy.\nThe president is elected indirectly through the Electoral College to a four-year term, along with the vice president. Under the Twenty-second Amendment, ratified in 1951, no person who has been elected to two presidential terms may be elected to a third. In addition, nine vice presidents have become president by virtue of a president's intra-term death or resignation. In all, 45 individuals have served 46 presidencies spanning 58 four-year terms. Joe Biden is the 46th and current president, having assumed office on January 20, 2021.\n\nPage: List of presidents of the United States\nSummary: The president of the United States is the head of state and head of government of the United States, indirectly elected to a four-year term via the Electoral College. The officeholder leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces. Since the office was established in 1789, 45 men have served in 46 presidencies. The first president, George Washington, won a unanimous vote of the Electoral College. Grover Cleveland served two non-consecutive terms and is therefore counted as the 22nd and 24th president of the United States, giving rise to the discrepancy between the number of presidencies and the number of individuals who have served as president.\nThe presidency of William Henry Harrison, who died 31 days after taking office in 1841, was the shortest in Ameri\nThought:"
  ]
}
[llm/end] [chain:AgentExecutor > chain:RunnableSequence > llm:Tongyi] [3.25s] Exiting LLM run with output:
{
  "generations": [
    [
      {
        "text": "I now know the final answer\nFinal Answer: 美国现任总统是乔·拜登（Joe Biden）。他于2021年1月20日就职，成为美国第46任总统。",
        "generation_info": {
          "finish_reason": "stop",
          "request_id": "5748aabc-67e8-9d4b-b639-ca9c253f21db",
          "token_usage": {
            "input_tokens": 988,
            "output_tokens": 47,
            "total_tokens": 1035
          }
        },
        "type": "Generation"
      }
    ]
  ],
  "llm_output": null,
  "run": null
}
[chain/start] [chain:AgentExecutor > chain:RunnableSequence > parser:ReActSingleInputOutputParser] Entering Parser run with input:
{
  "input": "I now know the final answer\nFinal Answer: 美国现任总统是乔·拜登（Joe Biden）。他于2021年1月20日就职，成为美国第46任总统。"
}
[chain/end] [chain:AgentExecutor > chain:RunnableSequence > parser:ReActSingleInputOutputParser] [0ms] Exiting Parser run with output:
[outputs]
[chain/end] [chain:AgentExecutor > chain:RunnableSequence] [3.35s] Exiting Chain run with output:
[outputs]
[chain/end] [chain:AgentExecutor] [16.87s] Exiting Chain run with output:
{
  "output": "美国现任总统是乔·拜登（Joe Biden）。他于2021年1月20日就职，成为美国第46任总统。"
}

{'input': '美国现任总统是谁？',
 'output': '美国现任总统是乔·拜登（Joe Biden）。他于2021年1月20日就职，成为美国第46任总统。'}

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通过以上简单的示例，我们就基本掌握了Agent的使用，是不是很简单~