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Build simple API service with Python FastAPI — Part 1

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Previously, I’ve written a blog for how to build API service with spring-boot.

In this series, I will walk through how to build API service (a blog API service) in FastAPI with Python.

In today part, I will cover what FastAPI is, SQLAlchemy for working with MySQL, and simple API to create a new user account.

I.What is FastAPI

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.6+ based on standard Python type hints.

The key features are:

Fast: Very high performance, on par with NodeJS and Go (thanks to Starlette and Pydantic). One of the fastest Python frameworks available.
Fast to code: Increase the speed to develop features by about 200% to 300% *.
Fewer bugs: Reduce about 40% of human (developer) induced errors. *
Intuitive: Great editor support. Completion everywhere. Less time debugging.
Easy: Designed to be easy to use and learn. Less time reading docs.
Short: Minimize code duplication. Multiple features from each parameter declaration. Fewer bugs.
Robust: Get production-ready code. With automatic interactive documentation.
Standards-based: Based on (and fully compatible with) the open standards for APIs: OpenAPI (previously known as Swagger) and JSON Schema.
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You can checkout more information from their official document page

II.Get started with “Hello {name}” with FastAPI:

1.Install FastApi:

To install FastAPI, simply use pip install fastapi

pip install fastapi
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You will also need uvicorn to run the server, so install uvicorn also

pip install uvicorn
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Above is how you install libraries in Python globally. But I would suggest you would install in your virtual environment.

For me I usually work with pipenv

So below is how to install library with pipenv

pipenv install {library_name}
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2.Implement API which return “Hello {name}”

First, just create the new Python project in your favorite IDE, then create a file like below

from fastapi import FastAPI

app = FastAPI()

async def root():
    return {"message": "Hello Donald"}
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To run this, simply :

uvicorn main:map
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The result will be like this when you open the url in your browser
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III. Build simple API to create new user account into your MySQL db

For doing this, first you need a way to connect to MySQL in Python.

We will be using SQLAlchemy with mysql-connector-python library.


SQLAlchemy is the Python SQL toolkit and Object Relational Mapper that gives application developers the full power and flexibility of SQL.

It provides a full suite of well known enterprise-level persistence patterns, designed for efficient and high-performing database access, adapted into a simple and Pythonic domain language.

You can find out more information for SQLAlchemy from here

To install SQLAlchemy:

pipenv install sqlalchemy
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MySQL-connector-python is a self-contained Python driver for communicating with MySQL servers, and how to use it to develop database applications.

You can find out more from the official page.

To install mysql-connector-python:

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3.Create a new database with table “user_info” in MySQL:

Create a database name “restapi”

USE restapi;
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Create a new table name “user_info”

CREATE TABLE user_info(
username VARCHAR(50) NOT NULL,
password VARCHAR(500) NOT NULL,
fullname VARCHAR(50) NOT NULL
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4.Create a new project for building the service with MySQL in Python

The new project will consists the following files:

- : to define method (read,write) to MySQL
- : for connecting MySQL
- main file for build FastAPI service
- define class object models for FastAPI
- define schemas for working with the specific API request/response
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from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

SQLALCHEMY_DATABASE_URL = "mysql+mysqlconnector://root:cuong1990@localhost:3306/restapi"

engine = create_engine(
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

Base = declarative_base()
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the database name will be : restapi

the username for database : root

the password for database : cuong1990

from sqlalchemy import Column, Integer, String
from sql_app.database import Base

class UserInfo(Base):
    __tablename__ = "user_info"

    id = Column(Integer, primary_key=True, index=True)
    username = Column(String, unique=True)
    password = Column(String)
    fullname = Column(String, unique=True)
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Define the class/object model for userinfo to interact with table “user_info”

from typing import List
from pydantic import BaseModel

class UserInfoBase(BaseModel):
    username: str
    fullname: str

class UserCreate(UserInfoBase):
    password: str

class UserInfo(UserInfoBase):
    id: int

    class Config:
        orm_mode = True
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Define the base schema and usercreate, userinfo schema for working with API request and response

from sqlalchemy.orm import Session

from . import models, schemas

def get_user_by_username(db: Session, username: str):
    return db.query(models.UserInfo).filter(models.UserInfo.username == username).first()

def create_user(db: Session, user: schemas.UserCreate):
    fake_hashed_password = user.password + "notreallyhashed"
    db_user = models.UserInfo(username=user.username, password=fake_hashed_password, fullname=user.fullname)
    return db_user
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Define the method for create new user and get user by username

from typing import List

import uvicorn
from sqlalchemy.orm import Session
from fastapi import Depends, FastAPI, HTTPException

from sql_app import models, schemas, crud
from sql_app.database import engine, SessionLocal


app = FastAPI()

# Dependency

def get_db():
    db = None
        db = SessionLocal()
        yield db
        db.close()"/user", response_model=schemas.UserInfo)
def create_user(user: schemas.UserCreate, db: Session = Depends(get_db)):
    db_user = crud.get_user_by_username(db, username=user.username)
    if db_user:
        raise HTTPException(status_code=400, detail="Username already registered")
    return crud.create_user(db=db, user=user)

if __name__ == "__main__":, host="", port=8081)
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Define for how to build api create_user and raise exception if create new username with username already.

To run the service with fastapi, you can easily run main file by clicking on green button
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Then you can see the service running:
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5.Interact with api using postman:

Create with username already existed:
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Create new user account successfully
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You can checkout sourcecode for this from github.

Happy coding ~~~

Top comments (1)

santosh profile image
Santosh Kumar

What is difference between yield vs return in get_db()?