Pythonあれこれ（Vol.78掲載）

著者：飯尾淳

本連載では「Pythonを昔から使っているものの、それほど使いこなしてはいない」という筆者が、いろいろな日常業務をPythonで処理することで、立派な「蛇使い」に育つことを目指します。その過程を温
かく見守ってください。皆さんと共に勉強していきましょう。第8回は、Webアプリケーションフレームワーク「Flask」を使って基本的なWebアプリを作成する方法を紹介します。データベースにアクセスする方法やテンプレートの利用方法も解説します。

シェルスクリプトマガジン Vol.78は以下のリンク先でご購入できます。

図1　「Hello World」に相当するシンプルなWebアプリのコード（app.py）

from flask import Flask

app = Flask(__name__)
@app.route('/')
def hello():
  return '<h1>Hello World!</h1>'

from flask import Flask

app = Flask(__name__)

@app.route('/')

def hello():

return '<h1>Hello World!</h1>'

図4　ルーティングの記述を追加したWebアプリのコード

from flask import Flask
app = Flask(__name__)

@app.route('/hello')
def hello():
  return '<h1>Hello World!</h1>'

@app.route('/goodbye')
def goodbye():
  return '<h1>Good-bye World!</h1>'

from flask import Flask

app = Flask(__name__)

@app.route('/hello')

def hello():

return '<h1>Hello World!</h1>'

@app.route('/goodbye')

def goodbye():

return '<h1>Good-bye World!</h1>'

図5　パスパラメータを使うWebアプリのコードの例

from flask import Flask
app = Flask(__name__)

@app.route('/hello/<name>')
def hello(name):
  return f'<h1>Hello {name}!</h1>'

from flask import Flask

app = Flask(__name__)

@app.route('/hello/<name>')

def hello(name):

return f'<h1>Hello {name}!</h1>'

図7　クエリーパラメータを使うWebアプリのコードの例

from flask import Flask, request
app = Flask(__name__)

@app.route('/hello')
def hello():
  name = request.args['name']
  return f'<h1>Hello {name}!</h1>'

from flask import Flask, request

app = Flask(__name__)

@app.route('/hello')

def hello():

name = request.args['name']

return f'<h1>Hello {name}!</h1>'

図9　メモ帳Webアプリのひな型コード

from flask import Flask, request
app = Flask(__name__)

@app.route('/addMemo')
def addMemo():
  name = request.args['name']
  description = request.args['description']
  return f'ADD: name = {name}, desc = {description}'

@app.route('/getMemo')
def getMemo():
  return f'[TBD]'

from flask import Flask, request

app = Flask(__name__)

@app.route('/addMemo')

def addMemo():

name = request.args['name']

description = request.args['description']

return f'ADD: name = {name}, desc = {description}'

@app.route('/getMemo')

def getMemo():

return f'[TBD]'

図10　データベースを使うメモ帳Webアプリのコード（その1）

from flask import Flask, request
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import Integer, String, Text

app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///memo.sqlite'

db = SQLAlchemy(app)

class Memo(db.Model):
  __tablename__ = 'memo'
  ID          = db.Column(Integer, primary_key=True)
  NAME        = db.Column(String(500))
  DESCRIPTION = db.Column(Text)

db.create_all()

@app.route('/addMemo')
def addMemo():
  name = request.args['name']
  description = request.args['description']
  return f'ADD: name = {name}, desc = {description}'

@app.route('/getMemo')
def getMemo():
  return f'[TBD]'

from flask import Flask, request

from flask_sqlalchemy import SQLAlchemy

from sqlalchemy import Integer, String, Text

app = Flask(__name__)

app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///memo.sqlite'

db = SQLAlchemy(app)

class Memo(db.Model):

__tablename__ = 'memo'

ID = db.Column(Integer, primary_key=True)

NAME = db.Column(String(500))

DESCRIPTION = db.Column(Text)

db.create_all()

@app.route('/addMemo')

def addMemo():

name = request.args['name']

description = request.args['description']

return f'ADD: name = {name}, desc = {description}'

@app.route('/getMemo')

def getMemo():

return f'[TBD]'

図12　データベースを使うメモ帳Webアプリのコード（その2）

from flask import Flask, request
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import Integer, String, Text

app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///memo.sqlite'

db = SQLAlchemy(app)

class Memo(db.Model):
  __tablename__ = 'memo'
  ID          = db.Column(Integer, primary_key=True)
  NAME        = db.Column(String(500))
  DESCRIPTION = db.Column(Text)

db.create_all()

@app.route('/addMemo')
def addMemo():
  name = request.args['name']
  description = request.args['description']
  db.session.add(Memo(NAME=name, DESCRIPTION=description))
  db.session.commit()
  db.session.close()
  return f'ADD: name = {name}, desc = {description}'

@app.route('/getMemo')
def getMemo():
  memos = db.session.query(
    Memo.ID, Memo.NAME, Memo.DESCRIPTION).all()
  return str(memos)

from flask import Flask, request

from flask_sqlalchemy import SQLAlchemy

from sqlalchemy import Integer, String, Text

app = Flask(__name__)

app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///memo.sqlite'

db = SQLAlchemy(app)

class Memo(db.Model):

__tablename__ = 'memo'

ID = db.Column(Integer, primary_key=True)

NAME = db.Column(String(500))

DESCRIPTION = db.Column(Text)

db.create_all()

@app.route('/addMemo')

def addMemo():

name = request.args['name']

description = request.args['description']

db.session.add(Memo(NAME=name, DESCRIPTION=description))

db.session.commit()

db.session.close()

return f'ADD: name = {name}, desc = {description}'

@app.route('/getMemo')

def getMemo():

memos = db.session.query(

Memo.ID, Memo.NAME, Memo.DESCRIPTION).all()

return str(memos)

図14　テンプレートファイル「index.html」の内容

<!DOCTYPE html>
<html>
  <head>
    <title>Flask Test</title>
  </head>
  <body>
    <h1>The Memo List</h1>
    <table>
      <tr><th>ID</th><th>Name</th><th>Description</th></tr>
      {% for memo in memos: %}
      <tr><td>{{ memo.0 }}</td>
          <td>{{ memo.1 }}</td>
          <td>{{ memo.2 }}</td></tr>
      {% endfor %}
    </table>
  </body>
</html>

<!DOCTYPE html>

<html>

<head>

<title>Flask Test</title>

</head>

<body>

<table>

<tr><th>ID</th><th>Name</th><th>Description</th></tr>

{% for memo in memos: %}

{% endfor %}

</table>

</body>

</html>

図15　テンプレートを使うメモ帳Webアプリのコード（その1）

from flask import Flask, request, render_template
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import Integer, String, Text

app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///memo.sqlite'

db = SQLAlchemy(app)

class Memo(db.Model):
  __tablename__ = 'memo'
  ID          = db.Column(Integer, primary_key=True)
  NAME        = db.Column(String(500))
  DESCRIPTION = db.Column(Text)

db.create_all()

@app.route('/addMemo')
def addMemo():
  name = request.args['name']
  description = request.args['description']
  db.session.add(Memo(NAME=name, DESCRIPTION=description))
  db.session.commit()
  db.session.close()
  return f'ADD: name = {name}, desc = {description}'

@app.route('/getMemo')
def getMemo():
  memos = db.session.query(
    Memo.ID, Memo.NAME, Memo.DESCRIPTION).all()
  return render_template('index.html', memos=memos)

from flask import Flask, request, render_template

from flask_sqlalchemy import SQLAlchemy

from sqlalchemy import Integer, String, Text

app = Flask(__name__)

app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///memo.sqlite'

db = SQLAlchemy(app)

class Memo(db.Model):

__tablename__ = 'memo'

ID = db.Column(Integer, primary_key=True)

NAME = db.Column(String(500))

DESCRIPTION = db.Column(Text)

db.create_all()

@app.route('/addMemo')

def addMemo():

name = request.args['name']

description = request.args['description']

db.session.add(Memo(NAME=name, DESCRIPTION=description))

db.session.commit()

db.session.close()

return f'ADD: name = {name}, desc = {description}'

@app.route('/getMemo')

def getMemo():

memos = db.session.query(

Memo.ID, Memo.NAME, Memo.DESCRIPTION).all()

return render_template('index.html', memos=memos)

図17　修正したテンプレートファイル「index.html」の内容

<!DOCTYPE html>
<html>
  <head>
    <title>Flask Test</title>
  </head>
  <body>
    <h1>The Memo List</h1>
    <table border="1" width="500" cellspacing="0"
           cellpadding="5" bordercolor="#333333">
      <tr><th>ID</th><th>Name</th><th>Description</th></tr>
      {% for memo in memos: %}
      <tr><td>{{ memo.0 }}</td>
          <td>{{ memo.1 }}</td>
          <td>{{ memo.2 }}</td></tr>
      {% endfor %}
    </table>
    <h2>New Memo</h2>
    <form action="/addMemo" method="post">
      <table style="text-align: left;">
        <tr style="vertical-align: top;"><th>Name:</th>
          <td><input type="text" name="name"></input></td></tr>
        <tr style="vertical-align: top;"><th>Description:</th>
          <td><textarea name="description" rows="4" cols="40">
              </textarea></td></td>
      </table>
      <input type="submit" value="Submit">
      <input type="reset" value="Reset">
    </form>
  </body>
</html>

<!DOCTYPE html>

<html>

<head>

<title>Flask Test</title>

</head>

<body>

<table border="1" width="500" cellspacing="0"

cellpadding="5" bordercolor="#333333">

<tr><th>ID</th><th>Name</th><th>Description</th></tr>

{% for memo in memos: %}

{% endfor %}

</table>

<tr style="vertical-align: top;"><th>Description:</th>

</textarea></td></td>

</table>

</form>

</body>

</html>

図18　テンプレートを使うメモ帳Webアプリのコード（その2）

from flask import Flask, request, render_template, redirect, url_for
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import Integer, String, Text

app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///memo.sqlite'

db = SQLAlchemy(app)

class Memo(db.Model):
  __tablename__ = 'memo'
  ID          = db.Column(Integer, primary_key=True)
  NAME        = db.Column(String(500))
  DESCRIPTION = db.Column(Text)

db.create_all()

@app.route('/addMemo', methods=['POST'])
def addMemo():
  name = request.form['name']
  description = request.form['description']
  db.session.add(Memo(NAME=name, DESCRIPTION=description))
  db.session.commit()
  db.session.close()
  return redirect(url_for('getMemo'))

@app.route('/getMemo')
def getMemo():
  memos = db.session.query(
    Memo.ID, Memo.NAME, Memo.DESCRIPTION).all()
  return render_template('index.html', memos=memos)

from flask import Flask, request, render_template, redirect, url_for

from flask_sqlalchemy import SQLAlchemy

from sqlalchemy import Integer, String, Text

app = Flask(__name__)

app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///memo.sqlite'

db = SQLAlchemy(app)

class Memo(db.Model):

__tablename__ = 'memo'

ID = db.Column(Integer, primary_key=True)

NAME = db.Column(String(500))

DESCRIPTION = db.Column(Text)

db.create_all()

@app.route('/addMemo', methods=['POST'])

def addMemo():

name = request.form['name']

description = request.form['description']

db.session.add(Memo(NAME=name, DESCRIPTION=description))

db.session.commit()

db.session.close()

return redirect(url_for('getMemo'))

@app.route('/getMemo')

def getMemo():

memos = db.session.query(

Memo.ID, Memo.NAME, Memo.DESCRIPTION).all()

return render_template('index.html', memos=memos)