✨ Add docs and tests for Python 3.9 and Python 3.10 (#3712)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>

docs_src/schema_extra_example/tutorial001_py310.py

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+from fastapi import FastAPI
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+class Item(BaseModel):
+    name: str
+    description: str | None = None
+    price: float
+    tax: float | None = None
+
+    class Config:
+        schema_extra = {
+            "example": {
+                "name": "Foo",
+                "description": "A very nice Item",
+                "price": 35.4,
+                "tax": 3.2,
+            }
+        }
+
+
+@app.put("/items/{item_id}")
+async def update_item(item_id: int, item: Item):
+    results = {"item_id": item_id, "item": item}
+    return results

docs_src/schema_extra_example/tutorial002_py310.py

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+from fastapi import FastAPI
+from pydantic import BaseModel, Field
+
+app = FastAPI()
+
+
+class Item(BaseModel):
+    name: str = Field(..., example="Foo")
+    description: str | None = Field(None, example="A very nice Item")
+    price: float = Field(..., example=35.4)
+    tax: float | None = Field(None, example=3.2)
+
+
+@app.put("/items/{item_id}")
+async def update_item(item_id: int, item: Item):
+    results = {"item_id": item_id, "item": item}
+    return results

docs_src/schema_extra_example/tutorial003_py310.py

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+from fastapi import Body, FastAPI
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+class Item(BaseModel):
+    name: str
+    description: str | None = None
+    price: float
+    tax: float | None = None
+
+
+@app.put("/items/{item_id}")
+async def update_item(
+    item_id: int,
+    item: Item = Body(
+        ...,
+        example={
+            "name": "Foo",
+            "description": "A very nice Item",
+            "price": 35.4,
+            "tax": 3.2,
+        },
+    ),
+):
+    results = {"item_id": item_id, "item": item}
+    return results

docs_src/schema_extra_example/tutorial004_py310.py

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+from fastapi import Body, FastAPI
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+class Item(BaseModel):
+    name: str
+    description: str | None = None
+    price: float
+    tax: float | None = None
+
+
+@app.put("/items/{item_id}")
+async def update_item(
+    *,
+    item_id: int,
+    item: Item = Body(
+        ...,
+        examples={
+            "normal": {
+                "summary": "A normal example",
+                "description": "A **normal** item works correctly.",
+                "value": {
+                    "name": "Foo",
+                    "description": "A very nice Item",
+                    "price": 35.4,
+                    "tax": 3.2,
+                },
+            },
+            "converted": {
+                "summary": "An example with converted data",
+                "description": "FastAPI can convert price `strings` to actual `numbers` automatically",
+                "value": {
+                    "name": "Bar",
+                    "price": "35.4",
+                },
+            },
+            "invalid": {
+                "summary": "Invalid data is rejected with an error",
+                "value": {
+                    "name": "Baz",
+                    "price": "thirty five point four",
+                },
+            },
+        },
+    ),
+):
+    results = {"item_id": item_id, "item": item}
+    return results