Build simple API service with Python FastAPI — Part 1

cuongld2 profile image cuongld2 ・5 min read

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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.

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

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

pip install uvicorn

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}

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

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

from fastapi import FastAPI

app = FastAPI()

async def root():
    return {"message": "Hello Donald"}

To run this, simply :

uvicorn main:map

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


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:


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

Create a database name “restapi”

USE restapi;

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

4.Create a new project for building the service with MySQL in Python

The new project will consists the following files:

- crud.py : to define method (read,write) to MySQL
- database.py : for connecting MySQL
- main.py: main file for build FastAPI service
- models.py: define class object models for FastAPI
- schemas.py: define schemas for working with the specific API request/response


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()

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)

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

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

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

@app.post("/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__":
    uvicorn.run(app, host="", port=8081)

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 ~~~

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Learning is hard work, but everything you learn is yours and will make subsequent learning easier. Medium page : https://medium.com/@ledinhcuong99


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