pip: "pip installs packages". Like npm --global in javascript

virtualenv

virtualenv: Creates an isolated working environment; enables side-by-side projects to work on different versions of python

pipenv: ties together pip and virtualenv to seem almost like npm and nvm working together.

It prevents pipenv from installing its virtual environments in a global area. Usually found in your shell init files like .bashrc, or .zshrc

pipfile

No! Only pipenv reads pipfiles.

1. Determine which version of python you want to run by running python versions
2. In your project directory, run the command: pipenv install --python "PYENV_ROOT/versions/3.8.1/bin/python" OR pipenv install --python <version>

1. Pipfile
2. Pipfile.lock
3. .venv directory

pipenv shell : You will notice you have a prompt prepended your your normal prompt, showing your project directory in parens

pytest : pipenv install pytest

pipenv uninstall <packageName>

pipenv install "pytest<=5.3"

pipenv run <programName>

1. Install pytest: pipinstall pytest
2. Execute: python -m unittest

import unittest

unittest.TestCase

__init__.py

Arrange, Act, and Assert

#Arrange area of your unittest function: s = Stack()

#Act: s.push()

#Assert: self.assertEqual(s.peek(), True) where s.peek() is a function that returns a boolean

Name them what they are testing for: "test_peek_returns_last_item_but_does_not_remove_it_from_stack"

    import unittest

    def TestStack(unittest.TestCase):
        def test_constructor_is_no_arg(self):
            #Arrange
            s = Stack()
            s.push(6.28)

            #Act
            result = s.pop()

            #Assert
            self.assertEqual(result, 6.28)

1. pipenv install --python 3.8.6
2. pipenv shell
3. pipenv install --dev pytest
4. Create a test folder name test
5. Add a __init__.py file to your test folder
6. You may need to update your virtual environment with a linter: pipenv install --dev pycodestyle then in VSCode choose linter of pycodestyle
7. pytest : to run pytest

If they begin with test, or end with test, then pytest understands it's a test file

    from stack import Stack  #import your class you're testing

    def test_peek_returns_last_item_pushed_but_leaves_it_on_stack():
        s = Stack()
        s.push(6.28)
        assert s.peek() == 6.28
        assert len(s) == 1

make sure they all begin with the word test. They can be camel cased - but must begin with the word "test"

• def test_push_increases_length_by_one():
• def testContructorIs_No_Arg():

Yes!

    import unittest
    from stack import Stack

    class TestStack(unittest.TestCase):
        def test_constructor_is_no_arg(self):
            #Arrange

            #Act
            Stack()

            #Assert

        def test_new_stack_has_zero_elements(self):
            #Arrange
            s = stack()

            #Act
            result = len(s)

            #Assert
            self.assertEqual(result,0)

use the @pytest.mark.skip() decorator above the function (or in unittest, the class). Note: You must import pytest to use the decorator.

Yes!

    def test_new_stack_has_zero_elements():
        if True:
            pytest.skiip()
        asert len(Stack()) == 0

A function that takes in another function to extend its behavior and return a modified version of the inner function

Dynamic modification through the use of Python decorators is a simple example of metaprogramming. Metaprogramming is when an object is created by other objects. Decorators are functions that return other functions.

The ability to examine objects to determine its behavior or type.

use the dir() function: print(dir(myFunction))
# ['__annotations__', '__call__', '__class__', '__closure__', '__code__', '__defaults__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__get__', '__getattribute__', '__globals__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__kwdefaults__', '__le__', '__lt__', '__module__', '__name__', '__ne__', '__new__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']

    def message_decorator(message_func):
        def message_wrapper(*args, **kwargs):
            message = message_func(kwargs['name'])
            author = kwargs['author']
            return f'{message}! This is a message from {author}.'
        return message_wrapper

1. The file object, such as opeining a file for reading: f = open('some_file.txt')
2. Database connections

    f = none
    try:
        f = open('some_file.txt')
        # do some stuff
    finally:
        if f:
            f.close()

with open('some_file.txt') as f:
    #do stuff with f like read the file

with psycopg2.connect(CONNECTION_PARAMETERS) as conn: with con.cursor() as curs: curs.execute(CREATE_USERS_TABLE_SQL)

1. __enter__
2. __exit__

    class WithLogger:
        def __enter__(self):
            print("2. In __enter__")
            return self

        def __exit__(self, type, value, traceback):
            print("4. In __exit__", type, value
            return True

    print("1. Before with")
    with WithLogger() as logger:
        print("3. In with block")
    print("5. After with")

This will print:

1. Before with
2. In __enter__
3. In with block
4. In __exit__ None None
5. After with

pipenv install psycopg2-binary

    CONNECTION_PARAMETERS = {
        'dbname': 'psycopg_test_db',
        'user': 'psycopg_test_user',
        'password': 'password',
    }

    import psycopg2

    CONNECTION_PARAMETERS = {
        'dbname': 'psycopg_test_db',
        'user': 'psycopg_test_user',
        'password': 'password',
    }

    #Connect to the database
    conn = psycopg2.connect(**CONNECTION_PARAMETERS)

    #Create a cursor
    curs = conn.cursor()

    #Do stuff ...

    #Commit the changes to the database
    conn.commit()

    #Close the connection
    curs.close()
    conn.close()

    import psycopg2

    CONNECTION_PARAMETERS = {
        'dbname': 'psycopg_test_db',
        'user': 'psycopg_test_user',
        'password': 'password',
    }

    def change_car_owner(car_id, new_owner_id):

        with psycopg2.connect(**CONNECTION_PARAMETERS) as conn:
            with conn.cursor() as curs:
                curs.execute("""
                            UPDATE cars SET owner_id = %(new_owner_id)s
                            WHERE id = %(car_id)s
                            """
                            {'car_id': car_id,
                            'new_owner_id': new_owner_id})

    change_car_owner(5, 1)
                    

1. pipenv install Flask~=1.1
2. pipenv install python-dotenv~=0.13 #to use the .flaskenv file

pipenv run flask --version

    from flask import Flask

    app = Flask(__name__)

    @app.route('/', methods=["GET", "POST"])
    def hello():
        return '
Hello, world!
'

In your .flaskenv file, create the following entries:

    FLASK_APP=<fileName>
    FLASK_ENV=development

pipenv run flask run

@app.route('/item/<id>') def item(id): return f'

Item {id}

    @app.route('/')
    @app.route('/home')
    def home():
        return '
Home
'

Use cases: opening a database connection or loading the logged-in user from the session.

    @app.before_request
    def before_request_function():
        print("before_request is running")

The function must take in the response as an argument, and must return a new, or the same response.

    @app.after_request
    def after_request_function(response):
        print("after_request is running")
        return response

Runs before the first request is handled:

    @app.before_first_request
    def before_first_function():
        print("before_first_request happens once"

pipenv install Jinja2~=2.11, then make sure all your .html files are inside a templates folder

from flask import render_template

    {% if not logged_in %}
        <a href="/login">Log in</a>
    {% endif %}

    <ul>
        {% for item in navigation %}
            <li>
                <a href="{{ item.href }}">{{ item.caption }}</a>
            </li>
        {% endfor %}
    </ul>

In copyright.html:

    © 2020 Me, myself, and I. All rights reserved.

    <a href="/">Home</a>
    |
    <a href="/about">About</a>

A SECRET_KEY

Because it is supposed to be secret, you should put it in your .env file

Use config.py:

    import os

    class Config(object):
        SECRET_KEY = os.environ.get('SECRET_KEY') or 'default-key-for-devs'

You need to use it in your route file:

    from flask import (Flask, render_template)
    from app.config import Config

    app = Flask(__name__)
    app.config.from_object(Config) #populate Flask config dictionary from config class

    pipenv install Flask~=1.1
    pipenv install Jinja2~=2.11
    pipenv install python-dotenv~=0.13
    pipenv install Flask-WTF~=0.14

1. Your html file : It will reference your form
2. A form.py file: Here you will instantiate your form class and define it
3. Your routes file: Here you will use your form class to access the form fields

    from flask_wtf import FlaskForm
    from wtforms import StringField, SelectField, BooleanField, SubmitField
    from wtforms.validators import DataRequired

    class SampleForm(FlaskForm):
        name = StringField('Name')

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