readme improvements (#109)

Author: samuelcolvin

README.md

@@ -40,7 +40,7 @@ PydanticAI is a Python Agent Framework designed to make it less painful to build
 * Novel, type-safe [dependency injection system](https://ai.pydantic.dev/dependencies/), useful for testing and eval-driven iterative development
 * [Logfire integration](https://ai.pydantic.dev/logfire/) for debugging and monitoring the performance and general behavior of your LLM-powered application
 
-## example "In Beta"
+## In Beta!
 
 PydanticAI is in early beta, the API is still subject to change and there's a lot more to do.
 [Feedback](https://github.com/pydantic/pydantic-ai/issues) is very welcome!
@@ -52,11 +52,16 @@ Here's a minimal example of PydanticAI:
 ```py
 from pydantic_ai import Agent
 
-agent = Agent(  # (1)!
+# Define a very simple agent including the model to use, you can also set the model when running the agent.
+agent = Agent(
     'gemini-1.5-flash',
+    # Register a static system prompt using a keyword argument to the agent.
+    # For more complex dynamically-generated system prompts, see the example below.
     system_prompt='Be concise, reply with one sentence.',
 )
 
+# Run the agent synchronously, conducting a conversation with the LLM.
+# Here the exchange should be very short: PydanticAI will send the system prompt and the user query to the LLM, the model will return a text response. See below for a more complex run.
 result = agent.run_sync('Where does "hello world" come from?')
 print(result.data)
 """
@@ -83,21 +88,29 @@ from pydantic_ai import Agent, RunContext
 from bank_database import DatabaseConn
 
 
+# SupportDependencies is used to pass data, connections, and logic into the model that will be needed when running
+# system prompt and tool functions. Dependency injection provides a type-safe way to customise the behavior of your agents.
 @dataclass
 class SupportDependencies:
     customer_id: int
     db: DatabaseConn
 
 
+# This pydantic model defines the structure of the result returned by the agent.
 class SupportResult(BaseModel):
     support_advice: str = Field(description='Advice returned to the customer')
     block_card: bool = Field(description="Whether to block the customer's card")
     risk: int = Field(description='Risk level of query', ge=0, le=10)
 
 
+# This agent will act as first-tier support in a bank.
+# Agents are generic in the type of dependencies they accept and the type of result they return.
+# In this case, the support agent has type `Agent[SupportDependencies, SupportResult]`.
 support_agent = Agent(
     'openai:gpt-4o',
     deps_type=SupportDependencies,
+    # The response from the agent will, be guaranteed to be a SupportResult,
+    # if validation fails the agent is prompted to try again.
     result_type=SupportResult,
     system_prompt=(
         'You are a support agent in our bank, give the '
@@ -106,30 +119,42 @@ support_agent = Agent(
 )
 
 
+# Dynamic system prompts can can make use of dependency injection.
+# Dependencies are carried via the `RunContext` argument, which is parameterized with the `deps_type` from above.
+# If the type annotation here is wrong, static type checkers will catch it.
 @support_agent.system_prompt
 async def add_customer_name(ctx: RunContext[SupportDependencies]) -> str:
     customer_name = await ctx.deps.db.customer_name(id=ctx.deps.customer_id)
     return f"The customer's name is {customer_name!r}"
 
 
+# `tool` let you register functions which the LLM may call while responding to a user.
+# Again, dependencies are carried via `RunContext`, any other arguments become the tool schema passed to the LLM.
+# Pydantic is used to validate these arguments, and errors are passed back to the LLM so it can retry.
 @support_agent.tool
 async def customer_balance(
     ctx: RunContext[SupportDependencies], include_pending: bool
-) -> str:
+) -> float:
     """Returns the customer's current account balance."""
+    # The docstring of a tool is also passed to the LLM as the description of the tool.
+    # Parameter descriptions are extracted from the docstring and added to the parameter schema sent to the LLM.
     balance = await ctx.deps.db.customer_balance(
         id=ctx.deps.customer_id,
         include_pending=include_pending,
     )
-    return f'${balance:.2f}'
+    return balance
 
 
-...
+...  # In a real use case, you'd add more tools and a longer system prompt
 
 
 async def main():
     deps = SupportDependencies(customer_id=123, db=DatabaseConn())
+    # Run the agent asynchronously, conducting a conversation with the LLM until a final response is reached.
+    # Even in this fairly simple case, the agent will exchange multiple messages with the LLM as tools are called to retrieve a result.
     result = await support_agent.run('What is my balance?', deps=deps)
+    # The result will be validated with Pydantic to guarantee it is a `SupportResult`, since the agent is generic,
+    # it'll also be typed as a `SupportResult` to aid with static type checking.
     print(result.data)
     """
     support_advice='Hello John, your current account balance, including pending transactions, is $123.45.' block_card=False risk=1

docs/index.md

@@ -95,13 +95,12 @@ async def add_customer_name(ctx: RunContext[SupportDependencies]) -> str:
 @support_agent.tool  # (6)!
 async def customer_balance(
     ctx: RunContext[SupportDependencies], include_pending: bool
-) -> str:
+) -> float:
     """Returns the customer's current account balance."""  # (7)!
-    balance = await ctx.deps.db.customer_balance(
+    return await ctx.deps.db.customer_balance(
         id=ctx.deps.customer_id,
         include_pending=include_pending,
     )
-    return f'${balance:.2f}'
 
 
 ...  # (11)!
@@ -127,8 +126,8 @@ async def main():
 3. The `SupportDependencies` dataclass is used to pass data, connections, and logic into the model that will be needed when running [system prompt](agents.md#system-prompts) and [tool](agents.md#function-tools) functions. PydanticAI's system of dependency injection provides a [type-safe](agents.md#static-type-checking) way to customise the behavior of your agents, and can be especially useful when running [unit tests](testing-evals.md) and evals.
 4. Static [system prompts](agents.md#system-prompts) can be registered with the [`system_prompt` keyword argument][pydantic_ai.Agent.__init__] to the agent.
 5. Dynamic [system prompts](agents.md#system-prompts) can be registered with the [`@agent.system_prompt`][pydantic_ai.Agent.system_prompt] decorator, and can make use of dependency injection. Dependencies are carried via the [`RunContext`][pydantic_ai.dependencies.RunContext] argument, which is parameterized with the `deps_type` from above. If the type annotation here is wrong, static type checkers will catch it.
-6. [`tool`](agents.md#function-tools) let you register functions which the LLM may call while responding to a user. Again, dependencies are carried via [`RunContext`][pydantic_ai.dependencies.RunContext], and any other arguments become the tool schema passed to the LLM. Pydantic is used to validate these arguments, and errors are passed back to the LLM so it can retry.
-7. The docstring of a tool is also passed to the LLM as the description of the tool. Parameter descriptions are [extracted](agents.md#function-tools-and-schema) from the docstring and added to the tool schema sent to the LLM.
+6. [`tool`](agents.md#function-tools) let you register functions which the LLM may call while responding to a user. Again, dependencies are carried via [`RunContext`][pydantic_ai.dependencies.RunContext], any other arguments become the tool schema passed to the LLM. Pydantic is used to validate these arguments, and errors are passed back to the LLM so it can retry.
+7. The docstring of a tool is also passed to the LLM as the description of the tool. Parameter descriptions are [extracted](agents.md#function-tools-and-schema) from the docstring and added to the parameter schema sent to the LLM.
 8. [Run the agent](agents.md#running-agents) asynchronously, conducting a conversation with the LLM until a final response is reached. Even in this fairly simple case, the agent will exchange multiple messages with the LLM as tools are called to retrieve a result.
 9. The response from the agent will, be guaranteed to be a `SupportResult`, if validation fails [reflection](agents.md#reflection-and-self-correction) will mean the agent is prompted to try again.
 10. The result will be validated with Pydantic to guarantee it is a `SupportResult`, since the agent is generic, it'll also be typed as a `SupportResult` to aid with static type checking.