change: optimize image build time in getting-started guide

docs/flask/Dockerfile

@@ -2,7 +2,8 @@ FROM python:3-slim
 WORKDIR /app
 ENV FLASK_APP=app.py
 ENV FLASK_RUN_HOST=0.0.0.0
-COPY . .
+COPY requirements.txt .
 RUN pip install -r requirements.txt
+COPY . .
 EXPOSE 5000
 CMD ["flask", "run"]

docs/flask/app.py

@@ -1,12 +1,11 @@
-import logging as log
 import os
 
 import psycopg2
 import redis
 from flask import Flask, render_template_string
 
 # HTML Jinja2 Template which will be shown in the browser
-page_template = '''
+page_template = """
         <div style="margin: auto; text-align: center;">
         <h1>{{ welcome_text }}</h1><br>
         <h2>This is a change :)</h2>
@@ -17,32 +16,37 @@
             {%- endfor %}
         </ul>
         </div>
-        '''
+        """
 
 # Defining the Flask Web App
 app = Flask(__name__)
-cache = redis.StrictRedis(host='cache', port=6379)
+cache = redis.StrictRedis(host="cache", port=6379)
 
 
 # The website root will show the page_template rendered with
 # - visitor count fetched from Redis Cache
 # - list of food fetched from Postgres DB
 # - welcome text passed in as environment variable
-@app.route('/')
+@app.route("/")
 def root():
     visitors = cache_get_visitor_count()
     food = db_get_squirrel_food()
 
-    return render_template_string(page_template, visitors=visitors, foods=food, welcome_text=os.getenv("WELCOME", "Hey Acorn user!"))
+    return render_template_string(
+        page_template,
+        visitors=visitors,
+        foods=food,
+        welcome_text=os.getenv("WELCOME", "Hey Acorn user!"),
+    )
 
 
 # Fetch the squirrel food from the Postgres database
 def db_get_squirrel_food():
     conn = psycopg2.connect(
         host="db",
         database="acorn",
-        user=os.environ['PG_USER'],
-        password=os.environ['PG_PASS'],
+        user=os.environ["PG_USER"],
+        password=os.environ["PG_PASS"],
     )
 
     cur = conn.cursor()
@@ -53,4 +57,4 @@ def db_get_squirrel_food():
 
 # Increment the visitor count in the Redis cache and return the new value
 def cache_get_visitor_count():
-    return cache.incr('visitors')
+    return cache.incr("visitors")