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Having fun with pydantic and pattern matching Sebastian Buczyński @ PyconPL 2024

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Sebastian Buczyński • Software Architect @ Sauce Labs • Trainer / Consultant @ Bottega IT Minds • I like memes • Blogger @ breadcrumbscollector.tech • Educate Pythonistas about software engineering whoami

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match latte: case Coffee() : print("It's caffee latte or latte machiato!") case Tea() : print("It's Matcha Latte") case _: print("Huh, no idea what it is”)

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match latte: case Coffee() : print("It's caffee latte or latte machiato!") case Tea() : print("It's Matcha Latte") case _: print("Huh, no idea what is it")

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match latte: case Coffee() : print("It's caffee latte or latte machiato!") case Tea() : print("It's Matcha Latte") case _: print("Huh, no idea what is it")

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price = 200 match price: ...

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price = 200 match price: case 100 : print("Cheap!") case 200 : print("Expensive!") case _: print("No idea")

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price = 200 match price: case 100 : print("Cheap!") case 200 : print("Expensive!") case _: print("No idea")

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price = 200 match price: case 100 : print("Cheap!") case 200 : print("Expensive!") case _: print("No idea")

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price = 200 match price: case 100 : print("Cheap!") case 200 : print("Expensive!") case _: print("No idea")

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price = 200 match price: case 100 : print("Cheap!") case 200 : print("Expensive!") case _: print("No idea") What we’ll see? #1

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price = 2137 match price: case 100 : print("Cheap!") case 200 : print("Expensive!") case _: print("No idea") What we’ll see? #2

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data = (1, 2, 3) match data: case {} : print("It's a dict!") case tuple() : print("Huh, a tuple!") case _: print("No idea") What we’ll see? #3

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data = {"name": "Sebastian"} match data: case {} : print("It's a dict!") case tuple() : print("Huh, a tuple!") case _: print("No idea") What we’ll see? #4

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What we’ll see? #5 data = {"name": "Sebastian"} match data: case {"name": _} : print("That's a dict with 'name'") case {} : print("It's a dict!") case _: print("No idea")

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What we’ll see? #6 data = {"name": "Sebastian"} match data: case {} : print("It's a dict!") case {"name": _} : print("That's a dict with 'name'") case _: print("No idea")

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What we’ll see? #6 data = {"name": "Sebastian"} match data: case {} : print("It's a dict!") case {"name": _} : print("That's a dict with 'name'") case _: print("No idea") Ordering of ‚cases’ is signi f icant

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@brock1137

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…just like with exceptions try: ... except Exception: ... except ValueError: ... # dead code!

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Match and assign name data = {"name": "Sebastian"} match data: case {"name": name} : print(f"That's a dict with 'name' = {name}") case _: print("No idea")

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Match multiple types using union data = {"price": 123} match data: case {"price": int() | float()} : print(f"That thing has a price tag on it!") case _: print("No idea")

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Match multiple patterns using union data = {"price": 123} match data: case {"name": _} | {"price": _} : print(f"It has a name or a price!") case _: print("No idea")

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Aliases on patterns data = {"name": "sebastian"} match data: case {"name": str() as name} : print(f"It has a name - {name}!") case _: print("No idea")

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guard clauses with „if” data = {"name": "sebastian"} match data: case {"name": str() as name} if name[0] == name[0].upper() : print(f"Hello! {name}!") case _: print("Name should start with a capital letter, mate!")

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No content

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Consuming stream of events

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Consuming stream of events: data {"type": "AccountCreated", "id": "64160ccb", "name": "Matthew"}

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Consuming stream of events: data {"type": "AccountCreated", "id": "64160ccb", "name": "Matthew"} {"type": "AccountUpdated", "id": "bb915f85", "old_status": "trial", "new_status": "paid"} {"type": "AccountDeleted", "id": "57ae55c5"}

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Consuming stream of events: data {"type": "AccountCreated", "id": "64160ccb", "name": "Matthew"} {"type": "AccountUpdated", "id": "bb915f85", "old_status": "trial", "new_status": "paid"} {"type": "AccountDeleted", "id": "57ae55c5"} {"type": "AccountUpdated", "id": "fede79b2", "old_status": "paid", "new_status": "trial"} {"type": "AccountCreated", "id": "23826148", "name": "John"}

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Consuming stream of events: data {"type": "AccountCreated", "id": "64160ccb", "name": "Matthew"} {"type": "AccountUpdated", "id": "bb915f85", "old_status": "trial", "new_status": "paid"} {"type": "AccountDeleted", "id": "57ae55c5"} {"type": "AccountUpdated", "id": "fede79b2", "old_status": "paid", "new_status": "trial"} {"type": "AccountCreated", "id": "23826148", "name": "John"} {"username": "Hecker"}

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def handle(payload: dict) -> None: ... # let's code this!

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def handle(payload: dict) -> None: # code like it's 2020 😎 if payload.get("type") == "AccountCreated": ... elif payload.get("type") == "AccountDeleted": ... elif payload.get("type") == "AccountUpdated": ... else: print("Omg, what is this?!")

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def handle(payload: dict) -> None: # code like it's 2020 😎 # ... and pretend we're in control 🙈🙉🙊 if payload.get("type") == "AccountCreated": ... elif payload.get("type") == "AccountDeleted": ... elif payload.get("type") == "AccountUpdated": if payload["new_status"] == "paid": ... elif payload["new_status"] == "trial": ... else: print("Omg, what is this?!")

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def handle(payload: dict) -> None: # HAMMER TIME! 🔨 match payload: case _: if payload.get("type") == "AccountCreated": ... elif payload.get("type") == "AccountDeleted": ... elif payload.get("type") == "AccountUpdated": if payload["new_status"] == "paid": ... elif payload["new_status"] == "trial": ... else: print("Omg, what is this?!")

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def handle(payload: dict) -> None: # HAMMER TIME! 🔨 match payload: case {"type": "AccountCreated"} : ... case _: if payload.get("type") == "AccountDeleted": ... elif payload.get("type") == "AccountUpdated": if payload["new_status"] == "paid": ... elif payload["new_status"] == "trial": ... else: print("Omg, what is this?!")

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def handle(payload: dict) -> None: # HAMMER TIME! 🔨 match payload: case {"type": "AccountCreated"} : ... case {"type": "AccountDeleted"} : ... case _: if payload.get("type") == "AccountUpdated": if payload["new_status"] == "paid": ... elif payload["new_status"] == "trial": ... else: print("Omg, what is this?!")

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def handle(payload: dict) -> None: # HAMMER TIME! 🔨 match payload: case {"type": "AccountCreated"} : ... case {"type": "AccountDeleted"} : ... case {"type": "AccountUpdated"} : if payload["new_status"] == "paid": ... elif payload["new_status"] == "trial": ... case _: print("Omg, what is this?!")

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def handle(payload: dict) -> None: # HAMMER TIME! 🔨 match payload: case {"type": "AccountCreated"} : ... case {"type": "AccountDeleted"} : ... case {"type": "AccountUpdated", "new_status": "paid"} : ... case {"type": "AccountUpdated", "new_status": "trial"} : ... case _: print("Omg, what is this?!")

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def handle(payload: dict) -> None: # HAMMER TIME! 🔨 match payload: case {"type": "AccountCreated"} : ... case {"type": "AccountDeleted"} : ... case {"type": "AccountUpdated", "new_status": "paid"} : ... case {"type": "AccountUpdated", "new_status": "trial"} : ... case _: print("Omg, what is this?!")

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Pydantic model {"type": "AccountCreated", "id": "64160ccb", "name": "Mateusz"}

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Pydantic model data = {"type": "AccountCreated", "id": "64160ccb", "name": "Matthew"} class AccountCreated(BaseModel) : type: str id: str name: str AccountCreated( ** data) # AccountCreated(type='AccountCreated', id='64160ccb', name='Matthew')

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Pydantic model with a constant data = {"type": "AccountCreated", "id": "64160ccb", "name": "Matthew"} class AccountCreated(BaseModel) : type: Literal["AccountCreated"] id: str name: str AccountCreated(type="BAZINGA", id=„64160ccb", name="Matthew") # raises exception

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Pydantic models class AccountCreated(BaseModel) : ... class AccountDeleted(BaseModel) : ... class AccountUpdated(BaseModel) : type: Literal["AccountUpdated"] id: str old_status: Literal["trial", "paid"] new_status: Literal["trial", "paid"]

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def handle(payload: dict) -> None: match payload: case {"type": "AccountCreated"} : ... case {"type": "AccountDeleted"} : ... case {"type": "AccountUpdated", "new_status": "paid"} : ... case {"type": "AccountUpdated", "new_status": "trial"} : ... case _: print("Omg, what is this?!")

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def handle(payload: dict) -> None: match payload: case {"type": "AccountCreated"} : event = AccountCreated( ** payload) case {"type": "AccountDeleted"} : event = AccountDeleted( ** payload) case {"type": "AccountUpdated", "new_status": "paid"} : event = AccountUpdated( ** payload) case {"type": "AccountUpdated", "new_status": "trial"} : event = AccountUpdated( ** payload) case _: print("Omg, what is this?!”)

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def handle(payload: dict) -> None: supported_model = ( AccountCreated | AccountDeleted | AccountUpdated ) match payload: case {"type": "AccountCreated"} : ...

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def handle(payload: dict) -> None: supported_model = ( AccountCreated | AccountDeleted | AccountUpdated ) adapter = TypeAdapter(supported_model) match payload: case {"type": "AccountCreated"} : ...

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def handle(payload: dict) -> None: supported_model = ( AccountCreated | AccountDeleted | AccountUpdated ) adapter = TypeAdapter(supported_model) event = adapter.validate_python(payload) # event will be an instance of a supported model! match payload: case {"type": "AccountCreated"} : ...

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def handle(payload: dict) -> None: supported_model = ( AccountCreated | AccountDeleted | AccountUpdated ) adapter = TypeAdapter(supported_model) event = adapter.validate_python(payload) match event: case AccountCreated() : ... case AccountUpdated(new_status="paid") : ... case AccountUpdated(new_status="trial") : ...

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def handle(payload: dict) -> None: supported_model = ( AccountCreated | AccountDeleted | AccountUpdated | Any ) adapter = TypeAdapter(supported_model) event = adapter.validate_python(payload) match event: case AccountCreated() : ... case AccountUpdated(new_status="paid") : ... case AccountUpdated(new_status="trial") : ... case _: print("Omg, what is this?!")

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def handle(payload: dict) -> None: supported_model = ( AccountCreated | AccountDeleted | AccountUpdated | Any ) adapter = TypeAdapter(supported_model) event = adapter.validate_python(payload) match event: case AccountCreated() : ... case AccountUpdated(new_status="paid") : ... case AccountUpdated(new_status="trial") : ... case _: print("Omg, what is this?!")

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def handle(payload: dict) -> None: supported_model = ( AccountCreated | AccountDeleted | AccountUpdated | Any ) adapter = TypeAdapter(supported_model) event = adapter.validate_python(payload) match event: case AccountCreated() : ... case AccountUpdated(new_status="paid") : ... case AccountUpdated(new_status="trial") : ... case _: print("Omg, what is this?!")

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class AccountUpdated(BaseModel) : type: Literal["AccountUpdated"] id: str old_status: Literal["trial", "paid"] new_status: Literal["trial", "paid"]

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class AccountUpdatedToPaid(BaseModel) : type: Literal["AccountUpdated"] id: str old_status: Literal["trial"] new_status: Literal["paid"] class AccountUpdatedToTrial(BaseModel) : type: Literal["AccountUpdated"] id: str old_status: Literal["paid"] new_status: Literal["trial"]

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def handle(payload: dict) -> None: supported_model = ( ... | Any ) adapter = TypeAdapter(supported_model) event = adapter.validate_python(payload) match event: case AccountCreated() : ... case AccountUpdatedToPaid() : ... case AccountUpdatedToTrial() : ... case _: print("Omg, what is this?!")

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import functools @functools.singledispatch def event_handler(event: Any) -> None: print("Omg, what is this?!")

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import functools @functools.singledispatch def event_handler(event: Any) -> None: print("Omg, what is this?!") @event_handler.register def handle_account_created(event: AccountCreated) -> None: ... @event_handler.register def handle_account_updated_to_paid(event: AccountUpdatedToPaid) -> None: ...

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ef handle(payload: dict) -> None: supported_model = ( AccountCreated | AccountDeleted | AccountUpdatedToTrial | AccountUpdatedToPaid | Any ) adapter = TypeAdapter(supported_model) event = adapter.validate_python(payload) event_handler(event)

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Recap

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match latte: case Coffee() : print("It's caffee latte or latte machiato!") case Tea() : print("It's Matcha Latte") case _: print("Huh, no idea what is it") match…case on types

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match event: case AccountCreated() : ... case AccountUpdated(new_status="paid") : ... case AccountUpdated(new_status="trial") : ... case _: print("Omg, what is this?!") match…case on attributes' values

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pattern matching using Pydantic class AccountCreated(BaseModel) : type: Literal["AccountCreated"] id: str name: str class AccountDeleted(BaseModel) : type: Literal["AccountDeleted"] id: str supported_model = ( AccountCreated | AccountDeleted | AccountUpdated ) adapter = TypeAdapter(supported_model) event = adapter.validate_python(payload)

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pattern matching using Pydantic class AccountCreated(BaseModel) : type: Literal["AccountCreated"] id: str name: str class AccountDeleted(BaseModel) : type: Literal["AccountDeleted"] id: str supported_model = ( AccountCreated | AccountDeleted | AccountUpdated | Any ) adapter = TypeAdapter(supported_model) event = adapter.validate_python(payload)

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Dispatch based on type using @singledispatch import functools @functools.singledispatch def event_handler(event: Any) -> None: print("Omg, what is this?!") @event_handler.register def handle_account_created(event: AccountCreated) -> None: ...

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Start writing classes 'cause types are awesome!

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Sebastian Buczyński breadcrumbscollector.tech Slides 👉

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Bonus Performance comparison • ifs are faster than match on dicts 5.22 times • match on dicts is faster than match on pydantic models 5.23 times • ifs are faster than match on pydantic models 27.28 times • ifs are faster than match on pydantic models with discriminant union 16.25 times Absolute times are: ifs: 2.0783760119229556e-07s match_dicts: 1.0846141958609223e-06s match_pydantic: 5.670525901950896e-06s match_pydantic_optimized: 3.377836011350155e-06s https://github.com/Enforcer/match-case-talk/blob/main/benchmark.py