Python ticketing example

patterns-use-cases/ticket-reservation/ticket-reservation-python/.gitignore

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+venv
+.venv
+__pycache__/

patterns-use-cases/ticket-reservation/ticket-reservation-python/README.md

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+# Restate Example: Ticket reservation system Python
+
+This example shows a subset of a ticket booking system.
+
+Restate is a system for easily building resilient applications using **distributed durable building blocks**.
+
+❓ Learn more about Restate from the [Restate documentation](https://docs.restate.dev).
+
+## Running the example
+
+To set up the example, use the following sequence of commands.
+
+Setup the virtual env:
+
+```shell
+python3 -m venv .venv
+source venv/bin/activate
+```
+
+Install the requirements:
+
+```shell
+pip install -r requirements.txt
+```
+
+Start the app as follows:
+
+```shell
+python3 -m hypercorn example/app:app
+```
+
+Start the Restate Server ([other options here]()):
+
+```shell
+restate-server
+```
+
+Register the service:
+
+```shell
+restate dp register http://localhost:8000
+```
+
+Then add a ticket to Mary's cart:
+
+```shell
+curl localhost:8080/cart/Mary/add_ticket -H 'content-type: application/json' -d '"seat2B"'
+```
+
+Let Mary buy the ticket via:
+```shell
+curl -X POST localhost:8080/cart/Mary/checkout
+```
+
+That's it! We managed to run the example, add a ticket to the user session cart, and buy it!

patterns-use-cases/ticket-reservation/ticket-reservation-python/example/app.py

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+import restate
+
+from example.cart_object import cart
+from example.checkout_service import checkout
+from example.ticket_object import ticket
+
+app = restate.app(services=[cart, checkout, ticket])

patterns-use-cases/ticket-reservation/ticket-reservation-python/example/cart_object.py

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+from datetime import timedelta
+
+from restate.context import ObjectContext
+from restate.object import VirtualObject
+
+from example.checkout_service import handle
+from example.ticket_object import reserve, mark_as_sold, unreserve
+
+cart = VirtualObject("cart")
+
+
+@cart.handler()
+async def add_ticket(ctx: ObjectContext, ticket_id: str) -> bool:
+    reserved = await ctx.object_call(reserve, key=ticket_id, arg=None)
+
+    if reserved:
+        tickets = await ctx.get("tickets") or []
+        tickets.append(ticket_id)
+        ctx.set("tickets", tickets)
+
+        ctx.object_send(expire_ticket, key=ctx.key(), arg=ticket_id, send_delay=timedelta(minutes=15))
+
+    return reserved
+
+
+@cart.handler()
+async def checkout(ctx: ObjectContext) -> bool:
+    tickets = await ctx.get("tickets") or []
+
+    if len(tickets) == 0:
+        return False
+
+    success = await ctx.service_call(handle, arg={'user_id': ctx.key(),
+                'tickets': tickets})
+
+    if success:
+        for ticket in tickets:
+            ctx.object_send(mark_as_sold, key=ticket, arg=None)
+
+        ctx.clear("tickets")
+
+    return success
+
+
+@cart.handler()
+async def expire_ticket(ctx: ObjectContext, ticket_id: str):
+    tickets = await ctx.get("tickets") or []
+
+    try:
+        ticket_index = tickets.index(ticket_id)
+    except ValueError:
+        ticket_index = -1
+
+    if ticket_index != -1:
+        tickets.pop(ticket_index)
+        ctx.set("tickets", tickets)
+
+        ctx.object_send(unreserve, key=ticket_id, arg=None)

patterns-use-cases/ticket-reservation/ticket-reservation-python/example/checkout_service.py

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+import uuid
+from typing import TypedDict, List
+from restate.context import ObjectContext, Serde
+from restate.service import Service
+
+from example.utils.email_client import EmailClient
+from example.utils.payment_client import PaymentClient
+
+
+class Order(TypedDict):
+    user_id: str
+    tickets: List[str]
+
+
+payment_client = PaymentClient()
+email_client = EmailClient()
+
+checkout = Service("checkout")
+
+
+@checkout.handler()
+async def handle(ctx: ObjectContext, order: Order) -> bool:
+    total_price = len(order['tickets']) * 40
+
+    idempotency_key = await ctx.run("idempotency_key", lambda: str(uuid.uuid4()))
+
+    async def pay():
+        return await payment_client.call(idempotency_key, total_price)
+    success = await ctx.run("payment", pay)
+
+    if success:
+        await ctx.run("send_success_email", lambda: email_client.notify_user_of_payment_success(order['user_id']))
+    else:
+        await ctx.run("send_failure_email", lambda: email_client.notify_user_of_payment_failure(order['user_id']))
+
+    return success

patterns-use-cases/ticket-reservation/ticket-reservation-python/example/ticket_object.py

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+from restate.context import ObjectContext
+from restate.object import VirtualObject
+
+
+ticket = VirtualObject("ticket")
+
+
+@ticket.handler()
+async def reserve(ctx: ObjectContext) -> bool:
+    status = await ctx.get("status") or "AVAILABLE"
+
+    if status == "AVAILABLE":
+        ctx.set("status", "RESERVED")
+        return True
+    else:
+        return False
+
+
+@ticket.handler()
+async def unreserve(ctx: ObjectContext):
+    status = await ctx.get("status") or "AVAILABLE"
+
+    if status != "SOLD":
+        ctx.clear("status")
+
+
+@ticket.handler()
+async def mark_as_sold(ctx: ObjectContext):
+    status = await ctx.get("status") or "AVAILABLE"
+
+    if status == "RESERVED":
+        ctx.set("status", "SOLD")

patterns-use-cases/ticket-reservation/ticket-reservation-python/example/utils/email_client.py

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+class EmailClient:
+
+    def __init__(self):
+        self.i = 0
+
+    def notify_user_of_payment_success(self, user_id: str):
+        print(f"Notifying user {user_id} of payment success")
+        # send the email
+        return True
+
+    def notify_user_of_payment_failure(self, user_id: str):
+        print(f"Notifying user {user_id} of payment failure")
+        # send the email
+        return True

patterns-use-cases/ticket-reservation/ticket-reservation-python/example/utils/payment_client.py

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+class PaymentClient:
+
+    def __init__(self):
+        self.i = 0
+
+    async def call(self, idempotency_key: str, amount: float) -> bool:
+        print(f"Payment call succeeded for idempotency key {idempotency_key} and amount {amount}")
+        # do the call
+        return True
+
+    async def failing_call(self, idempotency_key: str, amount: float) -> bool:
+        if self.i >= 2:
+            print(f"Payment call succeeded for idempotency key {idempotency_key} and amount {amount}")
+            i = 0
+            return True
+        else:
+            print(f"Payment call failed for idempotency key {idempotency_key} and amount {amount}. Retrying...")
+            self.i += 1
+            raise Exception("Payment call failed")

patterns-use-cases/ticket-reservation/ticket-reservation-python/requirements.txt

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+restate_sdk
+hypercorn