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How to install python and Flask on Mac OS X

#Starting Python Web development in Mac OS X#

Objective: Getting started with Python Development Operating System: Mac OS X Python version installed: 3.5 (5th December 2015)

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Mac OS uses default 2.x version out of box. To check whether, python has been installed successfully. try the following command.

python3 -V
Python 3.5.0

Above step ensure that Python 3.5 has been installed successfully.

This is the high level outline of this post: Mas OS X -> Python 3.5 -> Virtaulenv -> Flask --> Hello world )

Installing virtaulenv: (Step 1 of Why use virtualenv?

  1. Having different version of libraries for different projects
  2. Solves the elevated privillege issue as virtualenv allows you to install with user permission
    sudo pip3 install virtualenv
    virtualenv --version

Now lets create the first flask app

mkdir ~/projects
    cd ~/projects

Now we will create a virtualenv

virtualenv hello_flask
cd hello_flask

If you list the contents of the hello_flask directory, you will see that it has created several sub-directories, including a bin folder (Scripts on Windows) that contains copies of both Python and pip. The next step is to activate your new virtualenv.

source bin/activate

Installing Flask in your virtaulenv

pip install Flask

Hello, Flask

Create a new file called

from flask import Flask

app = Flask(__name__)

def index():
	return 'Hello, Flask!'

if __name__ == '__main__':

Open the web browser with http://localhost:5000

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Thank you!
A couple of notes for other people:

  • Create the file within the 'hello_flask' folder. It should should be on the same level as bin and include. (That's where I've got it anyway - and it works).
  • In your terminal - provided you've got all the above steps done and your current terminal position looks similar to this : (hello_flask) Alexs-MacBook-Pro-3:hello_flask Lord$, type python Then run the above localhost:5000 in your browser.

Thanks for the tip! It worked!

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i just want to add something very important
if it worked for you ... but you exit the terminal again if you come back it will says

File "/Library/Frameworks/Python.framework/Versions/3.8/bin/flask", line 6, in
from flask.cli import main
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/flask/", line 21, in
from .app import Flask
ModuleNotFoundError: No module named ''

*but you just need to repeat the activation which is

source bin/activate

then flask will run


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AtheerYahya commented Jun 15, 2020

I have a problem when running html code within I know where is the problem, the "return" should return something. here is my code:

from flask import Flask

app = Flask(name)

def home():
<!doctype html>


Hello Feroo!


if name =='main':
app.debug = True

if i did return 'hello world' it will work but that what i don't want. I want it to read the html code!

Any help is appreciated!!

P.s. I am using MacOS Catalina!!!!

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Thank you so much!!

  • Finally, a good example for Mac OS
Captura de pantalla 2024-03-01 a la(s) 2 35 17 p  m

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