Initial commit

.gitignore

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+# IDE
+.idea
+
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# Custom files
+*ready
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py,cover
+.hypothesis/
+.pytest_cache/
+cover/
+
+# Translations
+*.mo
+
+# Django stuff:
+*.log
+local_settings.py
+db.sqlite3
+db.sqlite3-journal
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+.pybuilder/
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+#   For a library or package, you might want to ignore these files since the code is
+#   intended to run in multiple environments; otherwise, check them in:
+# .python-version
+
+# pipenv
+#   According to pypa/pipenv#598, it is recommended to include Pipfile.lock in version control.
+#   However, in case of collaboration, if having platform-specific dependencies or dependencies
+#   having no cross-platform support, pipenv may install dependencies that don't work, or not
+#   install all needed dependencies.
+#Pipfile.lock
+
+# PEP 582; used by e.g. github.com/David-OConnor/pyflow
+__pypackages__/
+
+# Celery stuff
+celerybeat-schedule
+celerybeat.pid
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Spyder project settings
+.spyderproject
+.spyproject
+
+# Rope project settings
+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+.dmypy.json
+dmypy.json
+
+# Pyre type checker
+.pyre/
+
+# pytype static type analyzer
+.pytype/
+
+# Cython debug symbols
+cython_debug/

.pre-commit-config.yaml

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+repos:
+  - repo: https://github.com/pycqa/isort
+    rev: 5.10.1
+    hooks:
+      - id: isort
+        name: isort (python)
+        args:
+          - --profile=black
+  - repo: https://github.com/psf/black
+    rev: 22.6.0
+    hooks:
+      - id: black
+        language_version: python3
+        types: [ python ]
+  - repo: https://github.com/myint/autoflake
+    rev: v1.5.1
+    hooks:
+      - id: autoflake
+        language_version: python3
+        types: [ python ]
+        args:
+          - --remove-all-unused-imports
+          - --recursive
+          - --in-place

app/api.py

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+from typing import Optional
+
+from fastapi import FastAPI
+from pydantic import BaseModel, Field, condecimal, conint, constr, root_validator
+
+from app.types import Order, OrderSide, OrderType
+
+app = FastAPI()
+
+
+class CreateOrderModel(BaseModel):
+    type_: OrderType = Field(..., alias="type")
+    side: OrderSide
+    instrument: constr(min_length=12, max_length=12)
+    limit_price: Optional[condecimal(decimal_places=2)]
+    quantity: conint(gt=0)
+
+    @root_validator
+    def validator(cls, values: dict):
+        if values.get("type_") == "market" and values.get("limit_price"):
+            raise ValueError(
+                "Providing a `limit_price` is prohibited for type `market`"
+            )
+
+        if values.get("type_") == "limit" and not values.get("limit_price"):
+            raise ValueError("Attribute `limit_price` is required for type `limit`")
+
+        return values
+
+
+class CreateOrderResponseModel(Order):
+    pass
+
+
+@app.post(
+    "/orders",
+    status_code=201,
+    response_model=CreateOrderResponseModel,
+    response_model_by_alias=True,
+)
+async def create_order(model: CreateOrderModel):
+    # TODO: Add your implementation here
+    raise NotImplementedError()

app/stock_exchange.py

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+import random
+import time
+
+from app.types import Order
+
+
+class OrderPlacementError(Exception):
+    pass
+
+
+def place_order(order: Order):
+    """dummy function that is symbolic standing for placing an order at the stock exchange.
+    Please do not modify the content of this method."""
+
+    if not order:
+        raise ValueError("Required order parameter not provided")
+
+    if random.random() >= 0.9:
+        raise OrderPlacementError(
+            "Failed to place order at stock exchange. Connection not available"
+        )
+
+    # it is an expensive operation
+    time.sleep(0.5)

app/types.py

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+from datetime import datetime
+from enum import Enum
+from typing import Optional
+
+from pydantic import BaseModel, Field, condecimal, conint, constr
+
+
+class OrderSide(Enum):
+    BUY = "buy"
+    SELL = "sell"
+
+
+class OrderType(Enum):
+    MARKET = "market"
+    LIMIT = "limit"
+
+
+class Order(BaseModel):
+    # id generated by the database
+    id_: str = Field(..., alias="id")
+    created_at: datetime
+
+    type_: OrderType = Field(..., alias="type")
+    side: OrderSide
+    instrument: constr(min_length=12, max_length=12)
+    limit_price: Optional[condecimal(decimal_places=2)]
+    quantity: conint(gt=0)

readme.md

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+# Backend engineering task
+
+### Intro 
+
+The repository contains a bare setup for a REST API to place orders via a `POST - /orders` request, it can be found in [./app/api.py](./app/api.py).
+Additionally, it contains [a building block](./app/stock_exchange.py) that symbolizes placing an order at the stock exchange.
+
+The folder [tests](./tests) contains the setup for tests with the framework pytest.
+
+The challenge in this repository is a simplified version of what we are dealing with at lemon.markets 🍋. 
+
+## Your task
+
+We would like you to finalize the missing parts in this repository so that the following requirements are fulfilled:
+1. A valid request to `POST /orders` should result in the order being stored in a database of your choice.
+2. The created order should be placed at the stock exchange (use the method `place_order` provided in stock_exchange.py).
+3. The endpoint should return a status code of 201 and the created order details, provided that the order has been saved in the database **AND** it is guaranteed that the order **will** be placed on the stock exchange.  
+4. In the case of an error in the endpoint, it should return the status code 500 and the body `{"message": "Internal server error while placing the order"}` 
+5. The API should be highly scalable and reliable. The reliability of the provided stock exchange should not impact the reliability of the `POST /orders` endpoint
+
+
+Additionally, please add some tests and document how you would test the application as a whole and its pieces.
+For the implementation you can choose to use this Python setup or implement it in Javascript/Typescript.
+
+Please include a `solution.md` file where you document your decisions, assumptions, and also improvements you would like to incorporate in the future.
+
+We value your time ⏰, so we do not expect you to spend more than 4 hours preparing the solution. 🤗 
+Focus on implementing the main task first and afterwards jump on additional improvements as you see fit.
+
+### Bonus tasks
+* How would you change the system if we would receive a high volume of async updates to the orders placed through a socket connection on the stock exchange, e.g. execution information? Please outline the changes in the `solution.md`.
+* Feel free to add a GitHub actions workflow to test the application.
+* Feel free to add a Dockerfile.
+
+## Code quality
+
+In order to maintain a certain amount of code quality, we are using pre-commit hooks
+in this repository, which are installed by a 3rd-party tool called [pre-commit](https://pre-commit.com/).
+
+Please follow [this documentation](https://pre-commit.com/#install) to install `pre-commit`
+on your local machine. After that just execute the following command to install the hooks
+to your git folder:
+
+```shell
+pre-commit install
+```
+
+
+###  Everything process related
+Please create a fork or clone of this repository, commit all of your work to a new branch, and provide us with a link to the solution via mail 📩, at least 6h before the review meeting.

requirements-dev.txt

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+-r requirements.txt
+pytest
+pytest-cov
+pre-commit
+requests

requirements.txt

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+fastapi==0.85.0
+uvicorn[standard]==0.18.3
+pydantic==1.10.2

tests/conftest.py

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+import pytest as pytest
+from starlette.testclient import TestClient
+
+from app.api import app
+
+
+@pytest.fixture
+def client() -> TestClient:
+    return TestClient(app)