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use httpx.AsyncClient for async http requests #34

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Nov 25, 2024
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use httpx.AsyncClient for async http requests #34

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612d792
use httpx.AsyncClient for async http requests
graingert Nov 25, 2024
71bb5ba
use asyncio.run
graingert Nov 25, 2024
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102 changes: 62 additions & 40 deletions docs/first-server/python.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,7 @@ Let's build your first MCP server in Python! We'll create a weather server that

<Step title="Install additional dependencies">
```bash
uv add requests python-dotenv
uv add httpx python-dotenv
```
</Step>

Expand All @@ -69,7 +69,7 @@ Let's build your first MCP server in Python! We'll create a weather server that
from functools import lru_cache
from typing import Any

import requests
import httpx
import asyncio
from dotenv import load_dotenv
from mcp.server import Server
Expand Down Expand Up @@ -108,20 +108,20 @@ Let's build your first MCP server in Python! We'll create a weather server that
Add this functionality:

```python
# Create reusable session
http = requests.Session()
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There's nowhere to run a context manager and expose it to request handlers, so we're forced to create a new client each request: modelcontextprotocol/python-sdk#67

http.params = {
# Create reusable params
http_params = {
"appid": API_KEY,
"units": "metric"
}

async def fetch_weather(city: str) -> dict[str, Any]:
response = http.get(
f"{API_BASE_URL}/weather",
params={"q": city}
)
response.raise_for_status()
data = response.json()
async with httpx.AsyncClient() as client:
response = await client.get(
f"{API_BASE_URL}/weather",
params={"q": city, **http_params}
)
response.raise_for_status()
data = response.json()

return {
"temperature": data["main"]["temp"],
Expand Down Expand Up @@ -167,7 +167,7 @@ Let's build your first MCP server in Python! We'll create a weather server that
try:
weather_data = await fetch_weather(city)
return json.dumps(weather_data, indent=2)
except requests.RequestException as e:
except httpx.HTTPError as e:
raise RuntimeError(f"Weather API error: {str(e)}")

```
Expand Down Expand Up @@ -220,15 +220,17 @@ Let's build your first MCP server in Python! We'll create a weather server that
days = min(int(arguments.get("days", 3)), 5)

try:
response = http.get(
f"{API_BASE_URL}/{FORECAST_ENDPOINT}",
params={
"q": city,
"cnt": days * 8 # API returns 3-hour intervals
}
)
response.raise_for_status()
data = response.json()
async with httpx.AsyncClient() as client:
response = await client.get(
f"{API_BASE_URL}/{FORECAST_ENDPOINT}",
params={
"q": city,
"cnt": days * 8, # API returns 3-hour intervals
**http_params,
}
)
response.raise_for_status()
data = response.json()

forecasts = []
for i in range(0, len(data["list"]), 8):
Expand All @@ -245,7 +247,7 @@ Let's build your first MCP server in Python! We'll create a weather server that
text=json.dumps(forecasts, indent=2)
)
]
except requests.RequestException as e:
except requests.HTTPError as e:
logger.error(f"Weather API error: {str(e)}")
raise RuntimeError(f"Weather API error: {str(e)}")
```
Expand Down Expand Up @@ -443,9 +445,10 @@ Let's build your first MCP server in Python! We'll create a weather server that
<Card title="Error Handling" icon="shield">
```python
try:
response = self.http.get(...)
response.raise_for_status()
except requests.RequestException as e:
async with httpx.AsyncClient() as client:
response = await client.get(..., params={..., **http_params})
response.raise_for_status()
except requests.HTTPError as e:
raise McpError(
ErrorCode.INTERNAL_ERROR,
f"API error: {str(e)}"
Expand Down Expand Up @@ -565,12 +568,13 @@ uvicorn.run(app, host="0.0.0.0", port=8000)
last_cache_time is None or
now - last_cache_time > cache_timeout):

response = http.get(
f"{API_BASE_URL}/{CURRENT_WEATHER_ENDPOINT}",
params={"q": city}
)
response.raise_for_status()
data = response.json()
async with httpx.AsyncClient() as client:
response = await client.get(
f"{API_BASE_URL}/{CURRENT_WEATHER_ENDPOINT}",
params={"q": city, **http_params}
)
response.raise_for_status()
data = response.json()

cached_weather = {
"temperature": data["main"]["temp"],
Expand Down Expand Up @@ -674,6 +678,10 @@ uvicorn.run(app, host="0.0.0.0", port=8000)
DEFAULT_CITY
)

@pytest.fixture
def anyio_backend():
return "asyncio"

@pytest.fixture
def mock_weather_response():
return {
Expand Down Expand Up @@ -706,7 +714,7 @@ uvicorn.run(app, host="0.0.0.0", port=8000)
]
}

@pytest.mark.asyncio
@pytest.mark.anyio
async def test_fetch_weather(mock_weather_response):
with patch('requests.Session.get') as mock_get:
mock_get.return_value.json.return_value = mock_weather_response
Expand All @@ -720,7 +728,7 @@ uvicorn.run(app, host="0.0.0.0", port=8000)
assert weather["wind_speed"] == 3.6
assert "timestamp" in weather

@pytest.mark.asyncio
@pytest.mark.anyio
async def test_read_resource():
with patch('weather_service.server.fetch_weather') as mock_fetch:
mock_fetch.return_value = {
Expand All @@ -736,12 +744,26 @@ uvicorn.run(app, host="0.0.0.0", port=8000)
assert "temperature" in result
assert "clear sky" in result

@pytest.mark.asyncio
@pytest.mark.anyio
async def test_call_tool(mock_forecast_response):
with patch('weather_service.server.http.get') as mock_get:
mock_get.return_value.json.return_value = mock_forecast_response
mock_get.return_value.raise_for_status = Mock()
class Response():
def raise_for_status(self):
pass

def json(self):
return nock_forecast_response

class AsyncClient():
def __aenter__(self):
return self

async def __aexit__(self, *exc_info):
pass

async def get(self, *args, **kwargs):
return Response()

with patch('httpx.AsyncClient', new=AsyncClient) as mock_client:
result = await call_tool("get_forecast", {"city": "London", "days": 2})

assert len(result) == 1
Expand All @@ -751,14 +773,14 @@ uvicorn.run(app, host="0.0.0.0", port=8000)
assert forecast_data[0]["temperature"] == 18.5
assert forecast_data[0]["conditions"] == "sunny"

@pytest.mark.asyncio
@pytest.mark.anyio
async def test_list_resources():
resources = await list_resources()
assert len(resources) == 1
assert resources[0].name == f"Current weather in {DEFAULT_CITY}"
assert resources[0].mimeType == "application/json"

@pytest.mark.asyncio
@pytest.mark.anyio
async def test_list_tools():
tools = await list_tools()
assert len(tools) == 1
Expand All @@ -768,7 +790,7 @@ uvicorn.run(app, host="0.0.0.0", port=8000)
</Step>
<Step title="Run tests">
```bash
uv add --dev pytest pytest-asyncio
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httpx and starlette both depend on anyio which ships with an async test framework - so you don't need to install an extra one here

uv add --dev pytest
uv run pytest
```
</Step>
Expand Down