Create visitors_app.py

docs/tutorial/code/flask/visitors_app.py

@@ -0,0 +1,40 @@
+import datetime
+import os
+
+import flask
+import psycopg2
+
+app = flask.Flask(__name__)
+app.config.from_prefixed_env()
+
+DATABASE_URI = os.environ["POSTGRESQL_DB_CONNECT_STRING"]
+
+
+@app.route("/")
+def index():
+    with psycopg2.connect(DATABASE_URI) as conn, conn.cursor() as cur:
+        user_agent = flask.request.headers.get('User-Agent')
+        timestamp = datetime.datetime.now()
+
+        cur.execute(
+            "INSERT INTO visitors (timestamp, user_agent) VALUES (%s, %s)",
+            (timestamp, user_agent)
+        )
+        conn.commit()
+
+
+    greeting = app.config.get("GREETING", "Hello, world!")
+    return f"{greeting}\n"
+
+
+@app.route("/visitors")
+def visitors():
+    with psycopg2.connect(DATABASE_URI) as conn, conn.cursor() as cur:
+        cur.execute("SELECT COUNT(*) FROM visitors")
+        total_visitors = cur.fetchone()[0]
+
+    return f"{total_visitors}\n"
+
+
+if __name__ == "__main__":
+    app.run()