Added Flask-Demo and Flask AppBuilder tutorial

Flask-Demo/world.py

@@ -0,0 +1,51 @@
+"""Example web app that connects to PostgreSQL."""
+
+from io import StringIO
+
+import psycopg
+from flask import Flask
+
+app = Flask(__name__)
+con = psycopg.connect(
+    host="data.cs.jmu.edu", user="demo", password="demo", dbname="world"
+)
+cur = con.cursor()
+
+
+@app.route("/")
+def hello_world():
+    return "<p>Hello, World!</p>"
+
+
+@app.route("/country/<code>")
+def country_info(code: str):
+    _ = cur.execute(
+        "SELECT name, continent, region, population FROM country WHERE code = %s",
+        (code.upper(),),
+    )
+    row = cur.fetchone()
+    if not row:
+        return "<p>Country not found</p>"
+    name, cont, reg, pop = row
+    out = StringIO()
+    _ = out.write(
+        f"<p><strong>{name}</strong> is in <strong>{cont}</strong> in the <strong>{reg}</strong> region.</p>"
+    )
+    _ = out.write(
+        f"<p><strong>{name}</strong>'s population <strong>{pop:,d}</strong>.</p>"
+    )
+    return out.getvalue()
+
+
+@app.route("/codes")
+def multi_country():
+    _ = cur.execute("SELECT name, code population FROM country")
+
+    return f"<ul>{"".join(
+        f'<li><a href="/country/{code}">{name} {code}</a></li>'
+        for (name, code) in cur.fetchall()
+    )}</ul>"
+
+
+if __name__ == "__main__":
+    app.run(debug=True)