Day 2

Back to the basics: and, or, not, if

Before we do anything more interesting we're going to have to cover our logical basics. In Python these are not, and, or, and if.

Stop your server with ++ctrl++ + C
Type python in the terminal to open your python interpretor

not

Type x = True and press enter.
Type x and press enter to see that x is true.
Type not x and press enter. not inverts the value of x. So if x is True, not x is False.
Type not not x and press enter. not not x inverts not x. You can chain not as many times as you want.
Let's imagine we're building a weather app and we want to know if it's raining. Type is_raining = True and press enter.
Type print(f"should I wear a raincoat? {is_raining}") and press enter.
Today it's not raining. We could create a variable called is_not_raining but we could also just not. Type print(f"should I wear a raincoat? {not is_raining}")
Type not 'hello' and press enter. This might seem strange but Python interprets a string as True. not 'hello' will return False.
Type not '' and press enter. An empty string in Python is False. not '' returns True.

and

In your terminal type x = True and press enter.
Type x and press enter to see that x is True.
Type y = True and press enter.
Type y and press enter to see that y is True.
Type y and x and press enter. y is true and x is true, so y and x is true.
We're building our weather app to be more useful. We want to tell people if it's rainy and windy. Type rainy = True and press enter.
Type windy = True and press enter.
Type rainy and windy and press enter. We get True because it's rainy and windy.
Today it's not windy. Type rainy and not windy and press enter. We get False because it isn't rainy and windy.
Tomorrow it won't be windy and it also won't be rainy. Type not rainy and not windy and press enter. We get False because neither weather conditions are met.

or

In your terminal type x = True and press enter.
Type x and press enter to see that x is True.
Type y = False and press enter.
Type y and press enter to see that y is False.
Type y or x and press enter. x is True so asking if x or y is true will result in True.
Our weather app has millions of downloads. Our data suggests people don't like when it's cold or raining. Let's tell them when it's cold or raining.
Type cold = True and press enter.
Type raining = True and press enter.
Type cold or raining and press enter. We get True, it is cold and it is raining.
Today it isn't cold but it is raining. Type not cold or raining. We get True, it is still raining outside.
Tomorrow it won't be cold and it won't be raining. Type not cold or not raining. We get False because neither of our disliked weather conditions are met.

if

In your terminal type x = True and press enter.
Type x and press enter to see that x is True.
Type y = False and press enter.
Type y and press enter to see that y is False.
Type if x: and press enter. You'll see a .... Python is waiting for another input.
Type ++tab++ print('x is true!') and press enter. You should see another ....
Press enter again. 'x is true!' will print to the terminal.
Type if y: and press enter. Now type ++tab++ print('y is true!') and press enter twice. You won't see anything print.
Type if not y: and press enter. Now type ++tab++ print('y is false!') and press enter twice. You'll see 'y is false!') printed.
Now that our weather app is sentient let's give it some decision making capability.
Type raining = True and press enter.
Type if raining: and press enter.
Type ++tab++ print('You should wear a rain jacket') and press enter twice. Your weather app can now tell you to wear a jacket if it's raining outside.
Type exit() to exit

Building a Terrible Weather App

Create a new file called weather_app.py by clicking the "add file" icon in the top left of VSCode.
We're going to create an app where the user has to guess the weather. We're going to need the python random module to generate random weather conditions.
Add the following to the top of the page:
```
import random
```
This tells python we intend to use the random package
We'll generate 4 weather conditions. Add the following after import random
```
warm = random.choice([True, False])
cold = not warm
raining = random.choice([True, False])
snowing = not raining
```
random.choice([True, False]) selects either True or False randomly.

Let's print our weather conditions in a cryptic way. Add the following below our variables:

if warm or cold:
    print("It's warm or cold.")

if raining or warm:
    print("It's raining or warm.")

if raining or snowing:
    print("It's raining or snowing.")

if cold or snowing:
    print("It's cold or snowing.")

This will print weather conditions in pairs to make it more challenging for our users to guess the weather.

Now let's get our user input. Since we have 4 possible weather conditions we'll need 4 "guessing modules". Let's build the first one:
```
warm_guess = input("Is it warm? (y/n) ")
if warm_guess == 'y' and warm:
    print('Correct!')
elif warm_guess == 'n' and not warm:
    print('Correct!')
else:
    print('Wrong!')
```
We ask the user if it's warm. If they say 'y' and it is warm we tell them they got it right! If they guess wrong we tell them they are wrong.

We'll just repeat the guess module 3 more times for cold, raining, and snowing.

cold_guess = input("Is it cold? (y/n) ")
if cold_guess == 'y' and cold:
    print('Correct!')
elif cold_guess == 'n' and not cold:
    print('Correct!')
else:
    print('Wrong!')

raining_guess = input("Is it raining? (y/n) ")
if raining_guess == 'y' and raining:
    print('Correct!')
elif raining_guess == 'n' and not raining:
    print('Correct!')
else:
    print('Wrong!')

snowing_guess = input("Is it snowing? (y/n) ")
if snowing_guess == 'y' and snowing:
    print('Correct!')
elif snowing_guess == 'n' and not snowing:
    print('Correct!')
else:
    print('Wrong!')

Save with ++ctrl++ + S and run your weather app by typing python weather_app.py. Try to guess the weather.

Pulling it all together with some Django

Let's make a weather app! Open "views.py" by clicking on it.
At the top of views.py add the following:
```
import random
```

Now under all of our existing code in views.py add the following:

def weather(request):
    warm = random.choice([True, False])
    cold = not warm
    raining = random.choice([True, False])
    snowing = not raining

    if warm:
        temperature_report = "It's warm out! Don't wear a jacket."
    else:
        temperature_report = "It's cold out! Wear a jacket."

    if raining:
        precipitation_report = "It's raining! Bring an umbrella."
    else:
        precipitation_report = "It's snowing! Bring your skis."

    return render(
        request,
        "mysite/index.html",
        {"data": temperature_report + " " + precipitation_report}
    )