Flask Tutorial in Visual Studio Code

Flask is a lightweight Python framework for web applications that provides the basics for URL routing and page rendering.

Flask is called a "micro" framework because it doesn't directly provide features like form validation, database abstraction, authentication, and so on. Such features are instead provided by special Python packages called Flask extensions. The extensions integrate seamlessly with Flask so that they appear as if they were part of Flask itself. For example, Flask doesn't provide a page template engine, but installing Flask includes the Jinja templating engine by default. For convenience, we typically speak of these defaults as part of Flask.

In this Flask tutorial, you create a simple Flask app with three pages that use a common base template. Along the way, you experience a number of features of Visual Studio Code including using the terminal, the editor, the debugger, code snippets, and more.

The completed code project for this Flask tutorial can be found on GitHub:python-sample-vscode-flask-tutorial.

If you have any problems, you can search for answers or ask a question on thePython extension Discussions Q&A.

Prerequisites

To successfully complete this Flask tutorial, you must do the following (which are the same steps as in thegeneral Python tutorial):

1. Install thePython extension.

2. Install a version of Python 3 (for which this tutorial is written). Options include:

   • (All operating systems) A download frompython.org; typically use theDownload button that appears first on the page.
   • (Linux) The built-in Python 3 installation works well, but to install other Python packages you must runsudo apt install python3-pip in the terminal.
   • (macOS) An installation throughHomebrew on macOS usingbrew install python3.
   • (All operating systems) A download fromAnaconda (for data science purposes).

3. On Windows, make sure the location of your Python interpreter is included in your PATH environment variable. You can check the location by runningpath at the command prompt. If the Python interpreter's folder isn't included, open Windows Settings, search for "environment", selectEdit environment variables for your account, then edit thePath variable to include that folder.

Create a project environment for the Flask tutorial

In this section, you will create a virtual environment in which Flask is installed. Using a virtual environment avoids installing Flask into a global Python environment and gives you exact control over the libraries used in an application.

1. On your file system, create a folder for this tutorial, such ashello_flask.

2. Open this folder in VS Code by navigating to the folder in a terminal and runningcode ., or by running VS Code and using theFile >Open Folder command.

3. In VS Code, open the Command Palette (View >Command Palette or (⇧⌘P (Windows, LinuxCtrl+Shift+P))). Then select thePython: Create Environment command to create a virtual environment in your workspace. Selectvenv and then the Python environment you want to use to create it.

   Note: If you want to create an environment manually, or run into error in the environment creation process, visit theEnvironments page.

   

4. After your virtual environment creation has been completed, runTerminal: Create New Terminal (⌃⇧` (Windows, LinuxCtrl+Shift+`))) from the Command Palette, which creates a terminal and automatically activates the virtual environment by running its activation script.

   Note: On Windows, if your default terminal type is PowerShell, you may see an error that it cannot run activate.ps1 because running scripts is disabled on the system. The error provides a link for information on how to allow scripts. Otherwise, useTerminal: Select Default Profile to set "Command Prompt" or "Git Bash" as your default instead.

5. Install Flask in the virtual environment by running the following command in the VS Code Terminal:

   python -m pip install flask

You now have a self-contained environment ready for writing Flask code. VS Code activates the environment automatically when you useTerminal: Create New Terminal. If you open a separate command prompt or terminal, activate the environment by runningsource .venv/bin/activate (Linux/macOS) or.venv\Scripts\Activate.ps1 (Windows). You know the environment is activated when the command prompt shows(.venv) at the beginning.

Create and run a minimal Flask app

1. In VS Code, create a new file in your project folder namedapp.py using eitherFile >New from the menu, pressingCtrl+N, or using the new file icon in the Explorer View (shown below).

   

2. Inapp.py, add code to import Flask and create an instance of the Flask object. If you type the code below (instead of using copy-paste), you can observe VS Code'sIntelliSense and auto-completions:

   from flaskimport Flaskapp = Flask(__name__)

3. Also inapp.py, add a function that returns content, in this case a simple string, and use Flask'sapp.route decorator to map the URL route/ to that function:

   @app.route("/")def home():    return "Hello, Flask!"

   Tip: You can use multiple decorators on the same function, one per line, depending on how many different routes you want to map to the same function.

4. Save theapp.py file (⌘S (Windows, LinuxCtrl+S)).

5. In the Integrated Terminal, run the app by enteringpython -m flask run, which runs the Flask development server. The development server looks forapp.py by default. When you run Flask, you should see output similar to the following:

   (.venv)D:\py\\hello_flask>python -m flask run * Environment: production   WARNING: Do not use the development server in a production environment.   Use a production WSGI server instead. * Debug mode: off * Running on http://127.0.0.1:5000/ (PressCTRL+C to quit)

   If you see an error that the Flask module cannot be found, make sure you've runpython -m pip install flask in your virtual environment as described at the end of the previous section.

   Also, if you want to run the development server on a different IP address or port, use the host and port command-line arguments, as with--host=0.0.0.0 --port=80.

6. To open your default browser to the rendered page,Ctrl+click thehttp://127.0.0.1:5000/ URL in the terminal.

   

7. Observe that when you visit a URL like /, a message appears in the debug terminal showing the HTTP request:

   127.0.0.1 - - [11/Jul/201808:40:15] "GET / HTTP/1.1" 200 -

8. Stop the app by usingCtrl+C in the terminal.

Tip: When using a different filename thanapp.py, such aswebapp.py, you will need to define an environment variable named FLASK_APP and set its value to your chosen file. Flask's development server then uses the value of FLASK_APP instead of the default fileapp.py. For more information, seeFlask command line interface.

Run the app in the debugger

Debugging gives you the opportunity to pause a running program on a particular line of code. When a program is paused, you can examine variables, run code in the Debug Console panel, and otherwise take advantage of the features described onDebugging. Running the debugger also automatically saves any modified files before the debugging session begins.

Before you begin: Make sure you've stopped the running app at the end of the last section by usingCtrl+C in the terminal. If you leave the app running in one terminal, it continues to own the port. As a result, when you run the app in the debugger using the same port, the original running app handles all the requests and you won't see any activity in the app being debugged and the program won't stop at breakpoints. In other words, if the debugger doesn't seem to be working, make sure that no other instance of the app is still running.

1. Replace the contents ofapp.py with the following code, which adds a second route and function that you can step through in the debugger:

   import refrom datetimeimport datetimefrom flaskimport Flaskapp = Flask(__name__)@app.route("/")def home():    return "Hello, Flask!"@app.route("/hello/<name>")def hello_there(name):    now = datetime.now()    formatted_now = now.strftime("%A,%d %B, %Y at%X")    # Filter the name argument to letters only using regular expressions. URL arguments    # can contain arbitrary text, so we restrict to safe characters only.    match_object = re.match("[a-zA-Z]+", name)    if match_object:        clean_name = match_object.group(0)    else:        clean_name ="Friend"    content ="Hello there, " + clean_name +"! It's " + formatted_now    return content

   The decorator used for the new URL route,/hello/<name>, defines an endpoint /hello/ that can accept any additional value. The identifier inside< and> in the route defines a variable that is passed to the function and can be used in your code.

   URL routes are case-sensitive. For example, the route/hello/<name> is distinct from/Hello/<name>. If you want the same function to handle both, use decorators for each variant.

   As described in the code comments, always filter arbitrary user-provided information to avoid various attacks on your app. In this case, the code filters the name argument to contain only letters, which avoids injection of control characters, HTML, and so forth. (When you use templates in the next section, Flask does automatic filtering and you won't need this code.)

2. Set a breakpoint at the first line of code in thehello_there function (now = datetime.now()) by doing any one of the following:

   • With the cursor on that line, pressF9, or,
   • With the cursor on that line, select theRun >Toggle Breakpoint menu command, or,
   • Click directly in the margin to the left of the line number (a faded red dot appears when hovering there).

   The breakpoint appears as a red dot in the left margin:

   

3. Switch to theRun and Debug view in VS Code (using the left-side activity bar or⇧⌘D (Windows, LinuxCtrl+Shift+D)). You may see the message "To customize Run and Debug create a launch.json file". This means that you don't yet have alaunch.json file containing debug configurations. VS Code can create that for you if you click on thecreate a launch.json file link:

   

4. Select the link and VS Code will prompt for a debug configuration. SelectFlask from the dropdown and VS Code will populate a newlaunch.json file with a Flask run configuration. Thelaunch.json file contains a number of debugging configurations, each of which is a separate JSON object within theconfiguration array.

5. Scroll down to and examine the configuration, which is named "Python: Flask". This configuration contains"module": "flask",, which tells VS Code to run Python with-m flask when it starts the debugger. It also defines the FLASK_APP environment variable in theenv property to identify the startup file, which isapp.py by default, but allows you to easily specify a different file. If you want to change the host and/or port, you can use theargs array.

   {    "name":"Python Debugger: Flask",    "type":"debugpy",    "request":"launch",    "module":"flask",    "env": {        "FLASK_APP":"app.py",        "FLASK_DEBUG":"1"    },    "args": [        "run",        "--no-debugger",        "--no-reload"    ],    "jinja":true,    "justMyCode":true},

   Note: If theenv entry in your configuration contains"FLASK_APP": "${workspaceFolder}/app.py", change it to"FLASK_APP": "app.py" as shown above. Otherwise you may encounter error messages like "Cannot import module C" where C is the drive letter where your project folder resides.

   Note: Oncelaunch.json is created, anAdd Configuration button appears in the editor. That button displays a list of additional configurations to add to the beginning of the configuration list. (TheRun >Add Configuration menu command does the same action.).

6. Savelaunch.json (⌘S (Windows, LinuxCtrl+S)). In the debug configuration dropdown list select thePython: Flask configuration.

   

7. Start the debugger by selecting theRun >Start Debugging menu command, or selecting the greenStart Debugging arrow next to the list (F5):

   

   Observe that the status bar changes color to indicate debugging:

   

   A debugging toolbar (shown below) also appears in VS Code containing commands in the following order: Pause (or Continue,F5), Step Over (F10), Step Into (F11), Step Out (⇧F11 (Windows, LinuxShift+F11)), Restart (⇧⌘F5 (Windows, LinuxCtrl+Shift+F5)), and Stop (⇧F5 (Windows, LinuxShift+F5)). SeeVS Code debugging for a description of each command.

   

8. Output appears in a "Python Debug Console" terminal.Ctrl+click thehttp://127.0.0.1:5000/ link in that terminal to open a browser to that URL. In the browser's address bar, navigate tohttp://127.0.0.1:5000/hello/VSCode. Before the page renders, VS Code pauses the program at the breakpoint you set. The small yellow arrow on the breakpoint indicates that it's the next line of code to run.

   

9. Use Step Over to run thenow = datetime.now() statement.

10. On the left side of the VS Code window, you see aVariables pane that shows local variables, such asnow, as well as arguments, such asname. Below that are panes forWatch,Call Stack, andBreakpoints (seeVS Code debugging for details). In theLocals section, try expanding different values. You can also double-click values (or useEnter (Windows, LinuxF2)) to modify them. Changing variables such asnow, however, can break the program. Developers typically make changes only to correct values when the code didn't produce the right value to begin with.

    

11. When a program is paused, theDebug Console panel (which is different from the "Python Debug Console" in the Terminal panel) lets you experiment with expressions and try out bits of code using the current state of the program. For example, once you've stepped over the linenow = datetime.now(), you might experiment with different date/time formats. In the editor, select the code that readsnow.strftime("%A, %d %B, %Y at %X"), then right-click and selectEvaluate in Debug Console to send that code to the debug console, where it runs:

    now.strftime("%A, %d %B, %Y at %X")'Wednesday, 31 October, 2018 at 18:13:39'

    Tip: TheDebug Console also shows exceptions from within the app that may not appear in the terminal. For example, if you see a "Paused on exception" message in theCall Stack area ofRun and Debug view, switch to theDebug Console to see the exception message.

12. Copy that line into the > prompt at the bottom of the debug console, and try changing the formatting:

    now.strftime("%a, %d %B, %Y at %X")'Wed, 31 October, 2018 at 18:13:39'now.strftime("%a, %d %b, %Y at %X")'Wed, 31 Oct, 2018 at 18:13:39'now.strftime("%a, %d %b, %y at %X")'Wed, 31 Oct, 18 at 18:13:39'

13. Step through a few more lines of code, if you'd like, then select Continue (F5) to let the program run. The browser window shows the result:

    

14. Change the line in the code to use different datetime format, for examplenow.strftime("%a, %d %b, %y at %X"), and then save the file. The Flask server will automatically reload, which means the changes will be applied without the need to restart the debugger. Refresh the page on the browser to see the update.

15. Close the browser and stop the debugger when you're finished. To stop the debugger, use the Stop toolbar button (the red square) or theRun >Stop Debugging command (⇧F5 (Windows, LinuxShift+F5)).

Tip: To make it easier to repeatedly navigate to a specific URL likehttp://127.0.0.1:5000/hello/VSCode, output that URL using aprint statement. The URL appears in the terminal where you can useCtrl+click to open it in a browser.

Go to Definition and Peek Definition commands

During your work with Flask or any other library, you may want to examine the code in those libraries themselves. VS Code provides two convenient commands that navigate directly to the definitions of classes and other objects in any code:

• Go to Definition jumps from your code into the code that defines an object. For example, inapp.py, right-click on theFlask class (in the lineapp = Flask(__name__)) and selectGo to Definition (or useF12), which navigates to the class definition in the Flask library.

• Peek Definition (⌥F12 (WindowsAlt+F12, LinuxCtrl+Shift+F10), also on the right-click context menu), is similar, but displays the class definition directly in the editor (making space in the editor window to avoid obscuring any code). PressEscape to close the Peek window or use thex in the upper right corner.

  

Use a template to render a page

The app you've created so far in this tutorial generates only plain text web pages from Python code. Although it's possible to generate HTML directly in code, developers avoid such a practice because it opens the app tocross-site scripting (XSS) attacks. In thehello_there function of this tutorial, for example, one might think to format the output in code with something likecontent = "<h1>Hello there, " + clean_name + "!</h1>", where the result incontent is given directly to a browser. This opening allows an attacker to place malicious HTML, including JavaScript code, in the URL that ends up inclean_name and thus ends up being run in the browser.

A much better practice is to keep HTML out of your code entirely by usingtemplates, so that your code is concerned only with data values and not with rendering.

• A template is an HTML file that contains placeholders for values that the code provides at run time. The templating engine takes care of making the substitutions when rendering the page. The code, therefore, concerns itself only with data values and the template concerns itself only with markup.
• The default templating engine for Flask isJinja, which is installed automatically when you install Flask. This engine provides flexible options including automatic escaping (to prevent XSS attacks) and template inheritance. With inheritance, you can define a base page with common markup and then build upon that base with page-specific additions.

In this section, you create a single page using a template. In the sections that follow, you configure the app to serve static files, and then create multiple pages to the app that each contains a nav bar from a base template.

1. Inside thehello_flask folder, create a folder namedtemplates, which is where Flask looks for templates by default.

2. In thetemplates folder, create a file namedhello_there.html with the contents below. This template contains two placeholders named "name" and "date", which are delineated by pairs of curly braces,{{ and}}. As you can see, you can also include formatting code in the template directly:

   <!DOCTYPE html><html>    <head>        <meta charset="utf-8" />        <title>Hello, Flask</title>    </head>    <body>        {%if name %}            <strong>Hello there, {{ name }}!</strong> It's {{ date.strftime("%A, %d %B, %Y at %X") }}.        {% else %}            What's your name? Provide it after /hello/ in the URL.        {% endif %}    </body></html>

   Tip: Flask developers often use theflask-babel extension for date formatting, rather thanstrftime, as flask-babel takes locales and timezones into consideration.

3. Inapp.py, import Flask'srender_template function near the top of the file:

   from flaskimport render_template

4. Also inapp.py, modify thehello_there function to userender_template to load a template and apply the named values (and add a route to recognize the case without a name).render_template assumes that the first argument is relative to thetemplates folder. Typically, developers name the templates the same as the functions that use them, but matching names are not required because you always refer to the exact filename in your code.

   @app.route("/hello/")@app.route("/hello/<name>")def hello_there(name =None):    return render_template(        "hello_there.html",        name=name,        date=datetime.now()    )

   You can see that the code is now much simpler, and concerned only with data values, because the markup and formatting is all contained in the template.

5. Start the program (inside or outside of the debugger, using⌃F5 (Windows, LinuxCtrl+F5)), navigate to a /hello/name URL, and observe the results.

6. Also try navigating to a /hello/name URL using a name like<a%20value%20that%20could%20be%20HTML> to see Flask's automatic escaping at work. The "name" value shows up as plain text in the browser rather than as rendering an actual element.

Serve static files

Static files are of two types. First are those files like stylesheets to which a page template can just refer directly. Such files can live in any folder in the app, but are commonly placed within astatic folder.

The second type are those that you want to address in code, such as when you want to implement an API endpoint that returns a static file. For this purpose, the Flask object contains a built-in method,send_static_file, which generates a response with a static file contained within the app'sstatic folder.

The following sections demonstrate both types of static files.

Refer to static files in a template

1. In thehello_flask folder, create a folder namedstatic.

2. Within thestatic folder, create a file namedsite.css with the following contents. After entering this code, also observe the syntax highlighting that VS Code provides for CSS files, including a color preview:

   .message {    font-weight:600;    color:blue;}

3. Intemplates/hello_there.html, add the following line before the</head> tag, which creates a reference to the stylesheet.

   <link rel="stylesheet" type="text/css" href="{{ url_for('static', filename='site.css')}}" />

   Flask'surl_for tag that is used here, creates the appropriate path to the file. Because it can accept variables as arguments,url_for allows you to programmatically control the generated path, if desired.

4. Also intemplates/hello_there.html, replace the contents<body> element with the following markup that uses themessage style instead of a<strong> tag (and also displays a message if you just use a hello/ URL without a name):

   {%if name %}    <span class="message">Hello there, {{ name }}!</span> It's {{ date.strftime("%A, %d %B, %Y at %X") }}.{% else %}    <span class="message">What's your name? Provide it after /hello/ in the URL.</span>{% endif %}

5. Run the app, navigate to a /hello/name URL, and observe that the message renders in blue. Stop the app when you're done.

Serve a static file from code

1. In thestatic folder, create a JSON data file nameddata.json with the following contents (which are meaningless sample data):

   {  "01": {    "note":"This data is very simple because we're demonstrating only the mechanism."  }}

2. Inapp.py, add a function with the route /api/data that returns the static data file using thesend_static_file method:

   @app.route("/api/data")def get_data():    return app.send_static_file("data.json")

3. Run the app and navigate to the /api/data endpoint to see that the static file is returned. Stop the app when you're done.

Create multiple templates that extend a base template

Because most web apps have more than one page, and because those pages typically share many common elements, developers separate those common elements into a base page template that other page templates can then extend (this is also called template inheritance.)

Also, because you'll likely create many pages that extend the same template, it's helpful to create a code snippet in VS Code with which you can quickly initialize new page templates. A snippet helps you avoid tedious and error-prone copy-paste operations.

The following sections walk through different parts of this process.

Create a base page template and styles

A base page template in Flask contains all the shared parts of a set of pages, including references to CSS files, script files, and so forth. Base templates also define one or moreblock tags that other templates that extend the base are expected to override. A block tag is delineated by{% block <name> %} and{% endblock %} in both the base template and extended templates.

The following steps demonstrate creating a base template.

1. In thetemplates folder, create a file namedlayout.html with the contents below, which contains blocks named "title" and "content". As you can see, the markup defines a simple nav bar structure with links to Home, About, and Contact pages, which you will create in a later section. Each link again uses Flask'surl_for tag to generate a link at runtime for the matching route.

   <!DOCTYPE html><html>    <head>        <meta charset="utf-8" />        <title>{% block title %}{% endblock %}</title>        <link rel="stylesheet" type="text/css" href="{{ url_for('static', filename='site.css')}}" />    </head>    <body>        <div class="navbar">            <a href="{{ url_for('home') }}" class="navbar-brand">Home</a>            <a href="{{ url_for('about') }}" class="navbar-item">About</a>            <a href="{{ url_for('contact') }}" class="navbar-item">Contact</a>        </div>        <div class="body-content">            {% block content %}            {% endblock %}            <hr/>            <footer>                <p>&copy; 2018</p>            </footer>        </div>    </body></html>

2. Add the following styles tostatic/site.css, below the existing "message" style, and save the file. Note that this walkthrough doesn't attempt to demonstrate responsive design; these styles simply generate a reasonably interesting result.

   .navbar {    background-color:lightslategray;    font-size:1em;    font-family:'Trebuchet MS','Lucida Sans Unicode','Lucida Grande','Lucida Sans',Arial,sans-serif;    color:white;    padding:8px 5px 8px 5px;}.navbar a {    text-decoration:none;    color:inherit;}.navbar-brand {    font-size:1.2em;    font-weight:600;}.navbar-item {    font-variant:small-caps;    margin-left:30px;}.body-content {    padding:5px;    font-family:'Segoe UI',Tahoma, Geneva,Verdana,sans-serif;}

You can run the app at this point, but because you haven't made use of the base template anywhere and haven't changed any code files, the result is the same as the previous step. Complete the remaining sections to see the final effect.

Create a code snippet

Because the three pages you create in the next section extendlayout.html, it saves time to create acode snippet to initialize a new template file with the appropriate reference to the base template. A code snippet provides a consistent piece of code from a single source, which avoids errors that can creep in when using copy-paste from existing code.

1. In VS Code, selectFile >Preferences >Configure Snippets.

2. In the list that appears, selecthtml. The option may appear as "html.json" in theExisting Snippets section of the list if you've created snippets previously.

3. After VS Code openshtml.json, add the following entry within the existing curly braces (the explanatory comments, not shown here, describe details such as how the$0 line indicates where VS Code places the cursor after inserting a snippet):

   "Flask Tutorial: template extending layout.html": {    "prefix":"flextlayout",    "body": [        "{% extends\"layout.html\" %}",        "{% block title %}",        "$0",        "{% endblock %}",        "{% block content %}",        "{% endblock %}"    ],    "description":"Boilerplate template that extends layout.html"},

4. Save thehtml.json file (⌘S (Windows, LinuxCtrl+S)).

5. Now, whenever you start typing the snippet's prefix, such asflext, VS Code provides the snippet as an autocomplete option, as shown in the next section. You can also use theInsert Snippet command to choose a snippet from a menu.

For more information on code snippets in general, refer toCreating snippets.

Use the code snippet to add pages

With the code snippet in place, you can quickly create templates for the Home, About, and Contact pages.

1. In thetemplates folder, create a new file namedhome.html, Then start typingflext to see the snippet appear as a completion:

   

   When you select the completion, the snippet's code appears with the cursor on the snippet's insertion point:

   

2. At the insertion point in the "title" block, writeHome, and in the "content" block, write<p>Home page for the Visual Studio Code Flask tutorial.</p>, then save the file. These lines are the only unique parts of the extended page template:

3. In thetemplates folder, createabout.html, use the snippet to insert the boilerplate markup, insertAbout us and<p>About page for the Visual Studio Code Flask tutorial.</p> in the "title" and "content" blocks, respectively, then save the file.

4. Repeat the previous step to createtemplates/contact.html usingContact us and<p>Contact page for the Visual Studio Code Flask tutorial.</p> in the two content blocks.

5. Inapp.py, add functions for the /about/ and /contact/ routes that refer to their respective page templates. Also modify thehome function to use thehome.html template.

   # Replace the existing home function with the one below@app.route("/")def home():    return render_template("home.html")# New functions@app.route("/about/")def about():    return render_template("about.html")@app.route("/contact/")def contact():    return render_template("contact.html")

Run the app

With all the page templates in place, saveapp.py, run the app, and open a browser to see the results. Navigate between the pages to verify that the page templates are properly extending the base template.

Note: If you're not seeing the latest changes, you might need to do a hard refresh on the page to avoid seeing a cached file.

Optional activities

The following sections describe additional steps that you might find helpful in your work with Python and Visual Studio Code.

Create a requirements.txt file for the environment

When you share your app code through source control or some other means, it doesn't make sense to copy all the files in a virtual environment because recipients can always recreate the environment themselves.

Accordingly, developers typically omit the virtual environment folder from source control and instead describe the app's dependencies using arequirements.txt file.

Although you can create the file by hand, you can also use thepip freeze command to generate the file based on the exact libraries installed in the activated environment:

1. With your chosen environment selected using thePython: Select Interpreter command, run theTerminal: Create New Terminal command (⌃⇧` (Windows, LinuxCtrl+Shift+`))) to open a terminal with that environment activated.

2. In the terminal, runpip freeze > requirements.txt to create therequirements.txt file in your project folder.

Anyone (or any build server) that receives a copy of the project needs only to run thepip install -r requirements.txt command to reinstall the packages in the original environment. (The recipient still needs to create their own virtual environment, however.)

Note:pip freeze lists all the Python packages you have installed in the current environment, including packages you aren't currently using. The command also lists packages with exact version numbers, which you might want to convert to ranges for more flexibility in the future. For more information, seeRequirements Files in the pip command documentation.

Refactor the project to support further development

Throughout this Flask tutorial, all the app code is contained in a singleapp.py file. To allow for further development and to separate concerns, it's helpful to refactor the pieces ofapp.py into separate files.

1. In your project folder, create a folder for the app, such ashello_app, to separate its files from other project-level files likerequirements.txt and the.vscode folder where VS Code stores settings and debug configuration files.

2. Move thestatic andtemplates folders intohello_app, because these folders certainly contain app code.

3. In thehello_app folder, create a file namedviews.py that contains the routings and the view functions:

   from flaskimport Flaskfrom flaskimport render_templatefrom datetimeimport datetimefrom .import app@app.route("/")def home():    return render_template("home.html")@app.route("/about/")def about():    return render_template("about.html")@app.route("/contact/")def contact():    return render_template("contact.html")@app.route("/hello/")@app.route("/hello/<name>")def hello_there(name =None):    return render_template(        "hello_there.html",        name=name,        date=datetime.now()    )@app.route("/api/data")def get_data():    return app.send_static_file("data.json")

4. In thehello_app folder, create a file__init__.py with the following contents:

   import flaskapp = flask.Flask(__name__)

5. In thehello_app folder, create a filewebapp.py with the following contents:

   # Entry point for the application.from .import app# For application discovery by the 'flask' command.from .import views# For import side-effects of setting up routes.

6. Open the debug configuration filelaunch.json and update theenv property as follows to point to the startup object:

   "env": {    "FLASK_APP":"hello_app.webapp"},

7. Delete the originalapp.py file in the project root, as its contents have been moved into other app files.

8. Your project's structure should now be similar to the following:

   

9. Run the app in the debugger again to make sure everything works. To run the app outside of the VS Code debugger, use the following steps from a terminal:

   1. Set an environment variable forFLASK_APP. On Linux and macOS, useexport set FLASK_APP=webapp; on Windows use$env:FLASK_APP=webapp if you're using PowerShell, orset FLASK_APP=webapp if you're using Command Prompt.
   2. Navigate into thehello_app folder, then launch the program usingpython -m flask run.

Create a container for a Flask app using the Container Tools extension

TheContainer Tools extension makes it easy to build, manage, and deploy containerized applications from Visual Studio Code. If you're interested in learning how to create a Python container for the Flask app developed in this tutorial, check out thePython in a container tutorial, which will walk you through how to:

• Create aDockerfile file describing a simple Python container.
• Build, run, and verify the functionality of aFlask app.
• Debug the app running in a container.

If you have any problems, you can search for answers or ask a question on thePython extension Discussions Q&A.

Next steps

Congratulations on completing this walkthrough of working with Flask in Visual Studio Code!

The completed code project from this tutorial can be found on GitHub:python-sample-vscode-flask-tutorial.

Because this tutorial has only scratched the surface of page templates, refer to theJinja2 documentation for more information about templates. TheTemplate Designer Documentation contains all the details on the template language. You might also want to review theofficial Flask tutorial as well as the documentation for Flaskextensions.

To try your app on a production website, check out the tutorialDeploy Python apps to Azure App Service using Docker Containers. Azure also offers a standard container,App Service on Linux, to which you deploy web apps from within VS Code.

You may also want to review the following articles in the VS Code docs that are relevant to Python:

• Editing Python code
• Linting
• Managing Python environments
• Debugging Python
• Testing