Day 054

Udemy Python Bootcamp Day 054

Backend Web Development with Python

What Exactly is the Backend?

Client, Server, Database
These three components together will determine how your backend will work.

Client
This is the part that faces the user.

Server
Always ready to receive requests over the internet.

Database
Like a souped up spreadsheet where you are storing all the information related to your website.

Create Web Server with Flask

Flask is one of the most popular web development franeworks.
Framework is a little bit like a library in the sense that it's a package of code that you didn't write, but it also got some differences.
One of the biggest differences is the fact that a library is something which you call upon to do something specific. Whereas a framework is something which you have to abide by their rules, you have to use their architecture. And when it comes to triggering some sort of functionality, it's the framework that calls upon your code.
All we have to do is to plan ahead for certain situations.

from flask import Flask
app = Flask(__name__)


@app.route('/')
def hello_world():
    return 'Hello, World!'

私の小さくて貴重なHello World!

Understand the Command Line

The kernel refers to the actual program that interfaces with the hardware. So it's the core of your operating system.
The shall in computing refers to the user interface for you as a human to ba able to interact with the kernel and in turn with the hardware of your computer.
There's two variants to the shall. There are graphical user interface shells and there's also a command line interface. So this is an alternative way of interfacing with the kernel.
#Terminal

場所の変更、フォルダとファイルの作成/削除が可能
rm-rfを使用して削除する場合は特に注意してください.binにも残らない...

Special Attribute built into Python

from flask import Flask

app = Flask(__name__)

print(__name__)

#output
__main__

This name is one of the special attributes that's built into Python. You could tap into the name to find out what is the current class, function, method, or descriptor's name.
And when we get main , what it's telling us is basically we're executing the code in a particular module. So, that means it's run as a script or from an interactive prompt, but it's not run from an imported module.

from flask import Flask

app = Flask(__name__)


@app.route('/')
def hello_world():
    return 'Hello, World!'


if __name__ == "__main__":
    app.run()

Python Decorators

The syntax is code a Python decorator and this is something that you'll see in more advanced Python projects.

## Functions can have inputs/functionality/output
def add(n1, n2):
    return n1 + n2

def subtract(n1, n2):
    return n1 - n2

def multiply(n1, n2):
    return n1 * n2

def divide(n1, n2):
    return n1 / n2

##Functions are first-class objects, can be passed around as arguments e.g. int/string/float etc.

def calculate(calc_function, n1, n2):
    return calc_function(n1, n2)

result = calculate(add, 2, 3)
print(result)

##Functions can be nested in other functions

def outer_function():
    print("I'm outer")

    def nested_function():
        print("I'm inner")

    nested_function()

outer_function()

## Functions can be returned from other functions
def outer_function():
    print("I'm outer")

    def nested_function():
        print("I'm inner")

    return nested_function

inner_function = outer_function()
inner_function()

The first-class objects, can be passed around as arguments e.g. int/string/float etc.
The ability for us to treat functions as first-class objects basically means that we can pass them around as if they were just any other argument.

The @ Syntax

## Simple Python Decorator Functions
import time

def delay_decorator(function):
    def wrapper_function():
        time.sleep(2)
        #Do something before
        function()
        function()
        #Do something after
    return wrapper_function

@delay_decorator
def say_hello():
    print("Hello")

#With the @ syntactic sugar
@delay_decorator
def say_bye():
    print("Bye")

#Without the @ syntactic sugar
def say_greeting():
    print("How are you?")
decorated_function = delay_decorator(say_greeting)
decorated_function()

#output
(after 2 seconds,)
How are you?
How are you?

from flask import Flask

app = Flask(__name__)


@app.route('/')
def hello_world():
    return 'Hello, World!'

@app.route("/bye")
def say_bye():
    return "Bye"

if __name__ == "__main__":
    app.run()

Excercise

import time
# current_time = time.time()
# print(current_time)

def speed_calc_decorator(function):
    def wrapped_function():
        start_time = time.time()
        function()
        end_time = time.time()
        duration = end_time - start_time
        function_name = function.__name__
        print(f"The {function_name} took {duration} seconds.")
    return wrapped_function

@speed_calc_decorator
def fast_function():
    for i in range(10000000):
        i * i

@speed_calc_decorator      
def slow_function():
    for i in range(100000000):
        i * i

fast_function()
slow_function()

実はインストラクションを読んでも一番何をさせてくれるのか分からないので、ソリューションコードを見てみたかったのですが、クイズを見ました.
大天使亲自拍解决方案大天使亲自拍解决方案
動画を見てから作ったものですが.
大天使が実行したのは0.9秒6秒だったこの方法で私は5秒45秒だった速度差がこんなに大きい...?
エンコーディングルームからもっと早く出て

でもなぜかTypeErrorが表示される
馬鹿ですね.wrapped_functionを呼ぶときは()を貼ることはできませんが、貼るとなぜかタイプに出てきて、、、ふ
どうせ今日習ったフラスコが何をするか分からないが、歩いて見なければならない.see ya~