From 4e6a69c0380969bade40f55109584401a3a3924e Mon Sep 17 00:00:00 2001
From: ducoterra <ducoterra@gmail.com>
Date: Sun, 29 Nov 2020 14:46:34 -0500
Subject: [PATCH] day 4 done

---
 README.md     |   9 +-
 docs/day4.md  | 441 ++++++++++++++++++++++++++++++++++++++++++++++++++
 docs/index.md |   6 +-
 mkdocs.yml    |   1 +
 4 files changed, 455 insertions(+), 2 deletions(-)
 create mode 100644 docs/day4.md

diff --git a/README.md b/README.md
index 2a9a177..a15e2e7 100644
--- a/README.md
+++ b/README.md
@@ -1,8 +1,15 @@
 # Docs
 
+Converting mov to gif:
+
 ```bash
 ffmpeg -i in.mov -filter:v "setpts=0.5*PTS" out.gif
-ffmpeg -i in.mkv out.mov
+```
+
+Converting mkv to mp4 with 20Mbit bitrate
+
+```bash
+ffmpeg -i in.mkv -b:v 20M out.mov
 ```
 
 ```bash
diff --git a/docs/day4.md b/docs/day4.md
new file mode 100644
index 0000000..6911f48
--- /dev/null
+++ b/docs/day4.md
@@ -0,0 +1,441 @@
+# Day 4
+
+## "While"
+
+The last section covered the for loop - a useful loop when you have a finite number of things you need to do something with. A grocery list, api data, and application arguments could be massive but will always have a definite size. Let's talk about times when you don't know how many times to loop.
+
+### Example 1: A Game
+
+Let's imagine you're coding a checkers app. You might approach it like this:
+
+1. Game Start
+2. Player 1 moves
+3. Check if player 2 has no remaining pieces
+4. Player 2 moves
+5. Check if player 1 has no remaining pieces
+6. Player 1 moves
+7. Check if player 2 has no remaining pieces
+8. Player 2 moves
+9. Check if player 1 has no remaining pieces
+10. ""
+11. ""
+12. ""
+13. ...
+
+You'll need to do a lot of the same stuff over and over - that's great for a loop. Since you'll have no idea how long the game will go on you can't use a for loop because there aren't a finite number of things to loop through (although you could simple use [the longest checkers game](http://www.wylliedraughts.com/LongGame.htm#:~:text=The%20longest%20game%20that%20Wyllie,of%203%2Dmove%20restriction%20checkers.) as your starting point I suppose).
+
+What we need is a loop that run indefinitey until a condition is met - namely that one player wins the game.
+
+### Example 2: User Input
+
+Let's build a menu system for a text-based app.
+
+1. Open your python interpretor by typing `python` and pressing ++enter++
+2. In your python interpretor paste the following:
+
+    ```python
+    program_choices = ["print", "count", "add", "exit"]
+    while True:
+        choice = input(f"Please choose one of the following options: [{', '.join(program_choices)}]: ")
+        if choice == "print":
+            print("hello")
+        elif choice == "count":
+            print(", ".join(["1","2","3","4","5"]))
+        elif choice == "add":
+            num1 = input("first number: ")
+            num2 = input("second number: ")
+            try:
+                print(f"Answer: {int(num1) + int(num2)}")
+            except ValueError:
+                print("You did not provide 2 valid numbers")
+        elif choice == "exit":
+            break
+        else:
+            print("invalid choice!")
+    ```
+
+3. Exit the menu by typing 'exit'
+4. Type exit() to exit the python interpretor
+
+This lets a user select from a variety of options and returns them to the start of the menu upon a selection. If their selection is invalid we tell them it's invalid and return them to the start anyway. 
+
+Since we don't know how many things a user will want to do with our menu we should use a while loop to loop indefinitely.
+
+Note the line that says `break`. This is how you break out of a loop in python. as soon as you call `break` it will stop the loop.
+
+### Easy looping
+
+Now that we've seen a few examples let's run through the core of a while loop:
+
+1. Type `python` and press ++enter++ to open the python interpretor.
+2. We can use a while loop to do something indefinitely. Type the following and press ++enter++ twice:
+
+    ```python
+    while True:
+        print("hello")
+    ```
+
+3. Press ++ctrl+c++ to stop the loop
+4. We can use a while loop like a for loop (though this isn't recommended - it's too easy to get stuck in an infinite loop). Type the following and press ++enter++ twice:
+
+    ```python
+    count_to = 10
+    start_at = 1
+    while start_at <= count_to:
+        print(start_at)
+        start_at += 1
+    ```
+
+5. We can use a while loop to check multiple conditions. Type the following and press ++enter++:
+
+    ```python
+    import random
+    day = 1
+    raining = True
+    temperature = "cold"
+    while temperature == "cold" or raining == True:
+        print(f"Day {day}: Stay inside")
+        day += 1
+        temperature = random.choice(["cold", "warm"])
+        raining = random.choice([True, False])
+
+    print(f"Day {day}: It's safe")
+    ```
+
+6. We can put while loops inside while loops (notice how we break out of each loop - this requires 2 break statements). Type the following and press ++enter++:
+
+    ```python
+    while True:
+        print("loop 1")
+        while True:
+            print("loop 2")
+            break
+        break
+    ```
+
+## Let's build a menu
+
+We're going to build a piece of software that lets us interact with our people API. We should be able to:
+
+1. List the people from our API
+2. Update the list by calling the API
+3. Clear the list
+4. Exit
+
+Let's get started:
+
+1. Create a new file in your root directory called "menu.py"
+2. Add the following to the top:
+
+    ```python
+    import requests
+    import json
+    ```
+
+3. Create the list_people function by adding the following:
+
+    ```python hl_lines="5-7"
+    import requests
+    import json
+
+    def list_people(people):
+        print(people)
+        return people
+    ```
+
+4. Now create the update_people function by adding the following:
+
+    ```python hl_lines="5-12"
+    def list_people(people):
+        print(people)
+        return people
+
+    def update_people(people):
+        try:
+            response = requests.get("http://localhost:8000/people")
+            people = response.json()["data"]
+            print("successfully updated people.")
+        except requests.exceptions.ConnectionError:
+            print("Server is not running. Failed to update.")
+        return people
+    ```
+
+5. Now create the clear_people function by adding the following:
+
+    ```python hl_lines="10-12"
+    def update_people(people):
+        try:
+            response = requests.get("http://localhost:8000/people")
+            people = response.json()["data"]
+            print("successfully updated people.")
+        except requests.exceptions.ConnectionError:
+            print("Server is not running. Failed to update.")
+        return people
+
+    def clear_people(people):
+        people = None
+        return people
+    ```
+
+6. Finally add the main loop:
+
+    ```python hl_lines="5-19"
+    def clear_people(people):
+        people = None
+        return people
+
+    if __name__ == "__main__":
+        people = None
+        choices = ["list", "update", "clear", "exit"]
+        while True:
+            choice = input(f"Please choose an option [{', '.join(choices)}]: ")
+            if choice == "list":
+                people = list_people(people)
+            elif choice == "update":
+                people = update_people(people)
+            elif choice == "clear":
+                people = clear_people(people)
+            elif choice == "exit":
+                break
+            else:
+                print("Invalid choice. Please try again.")
+    ```
+
+7. Check your work. Your whole program should be 35 lines long and look like this:
+
+    ```python
+    import requests
+    import json
+
+    def list_people(people):
+        print(people)
+        return people
+
+    def update_people(people):
+        try:
+            response = requests.get("http://localhost:8000/people")
+            people = response.json()["data"]
+            print("successfully updated people.")
+        except requests.exceptions.ConnectionError:
+            print("Server is not running. Failed to update.")
+        return people
+
+    def clear_people(people):
+        people = None
+        return people
+
+    if __name__ == "__main__":
+        people = None
+        choices = ["list", "update", "clear", "exit"]
+        while True:
+            choice = input(f"Please choose an option [{', '.join(choices)}]: ")
+            if choice == "list":
+                people = list_people(people)
+            elif choice == "update":
+                people = update_people(people)
+            elif choice == "clear":
+                people = clear_people(people)
+            elif choice == "exit":
+                break
+            else:
+                print("Invalid choice. Please try again.")
+    ```
+
+8. Run the program by typing `python menu.py` and pressing ++enter++.
+9. Type "list" and press ++enter++. You should see "None" printed to the screen. We haven't updated our people yet!
+10. Type "update" and press ++enter++. You should see "Server is not running. Failed to update.". We didn't run our server!
+11. Open a new terminal by clicking the plus icon.
+12. Type `python manage.py runserver` and press ++enter++.
+13. Flip back over to your other terminal by using the dropdown menu.
+14. Type "update" and press ++enter++. You should see "successfully updated people."
+15. Type "list" again and press ++enter++. You should see your people print out.
+16. Type "clear" and press ++enter++.
+17. Type "list" again and press ++enter++. Your people should be cleared.
+18. Type "exit" to exit.
+19. Flip back over to your django terminal with the dropdown menu
+20. Press ++ctrl+c++ to stop the server
+
+### Threading
+
+One of the more difficult concepts in programming is threading and multiprocessing. It's rarely taught at an intro level but it's fairly easy to use.
+
+A program runs in a "thread". When you run `python menu.py` it creates one thread that executes all code in order. Code at the end of your file can't run before code at the beginning of your file.
+
+...unless it could. What if you have a super slow internet connection and you need to make an api call? You don't want it to slow down your whole menu.
+
+Here's the idea: we tell our computer to make the slow call to our API in the background and continue letting the user mess with the menu.
+
+Let's make that a reality by simulating a slow internet connection.
+
+1. Open views.py
+2. For this part we're going to need the time library. "time" lets us pause code execution for a bit, simulating a slow internet. At the top of views.py add the following:
+
+    ```python hl_lines="2 2"
+    import random
+    import time
+    from django.shortcuts import render
+    from django.http import JsonResponse
+    ```
+
+3. Jump to the very bottom and add the highlighted code:
+
+    ```python hl_lines="10-23"
+    def api(request):
+        people = [
+            {"first name" : "Jim", "last name": "Fowler", "age": 24},
+            {"first name" : "Bob", "last name": "Jones", "age": 36},
+            {"first name" : "Alice", "last name": "Appleseed", "age": 52}
+        ]
+
+        return JsonResponse({"data": people})
+
+    def slow_api(request):
+        people = []
+        first_names = ["Liam", "Noah", "Oliver", "William", "Olivia", "Emma", "Ava", "Sophia", "Isabella"]
+        last_names = ["Smith", "Johnson", "Anderson", "Brown", "Garcia", "Miller", "Martinez", "Chavez"]
+        num_people = random.randint(1,100)
+        
+        for person in range(num_people):
+            time.sleep(.1)
+            first_name = random.choice(first_names)
+            last_name = random.choice(last_names)
+            age = random.randint(1,100)
+            people.append({"first_name": first_name, "last_name": last_name, "age": age})
+        
+        return JsonResponse({"data": people})
+    ```
+
+4. Save with ++ctrl+s++
+5. We need to add a URL, open urls.py
+6. Add the highlighted code:
+
+    ```python hl_lines="8 8"
+    from django.urls import path
+    from . import views
+
+    urlpatterns = [
+        path('', views.index),
+        path('weather/', views.weather),
+        path('people/', views.api),
+        path('slow/', views.slow_api),
+    ]
+    ```
+
+7. Save with ++ctrl+s++
+8. Open a new terminal by clicking the plus icon.
+9.  Type `python manage.py runserver` and press ++enter++.
+10. Flip back over to your other terminal by using the dropdown menu.
+11. Navigate to <http://localhost:8000/slow/> to see your api results. Notice how long the page takes to load.
+12. Let's try our menu.py with the new API. Open menu.py and update line 10:
+
+    ```python hl_lines="3 3"
+    def update_people(people):
+    try:
+        response = requests.get("http://localhost:8000/slow")
+        people = response.json()["data"]
+        print("successfully updated people.")
+    ```
+
+13. Save with ++ctrl+s++
+14. Open a new terminal by clicking the plus icon
+15. Type `python menu.py` and press ++enter++
+16. Type "list" and press ++enter++. You should see `None`
+17. Type "update" and press ++enter++. Notice the delay. While we're waiting for our api to respond our menu won't respond to any thing we type.
+18. Type "exit" to exit.
+19. Let's add the magic that will unblock our menu during an API call. At the top of menu.py add the following:
+
+    ```python hl_lines="3 3"
+    import requests
+    import json
+    import concurrent.futures import ThreadPoolExecutor
+    ```
+
+20. We need to modify our main program to call the update_people function in a different thread. To do this we need to keep track of a "future" object.
+
+    A future is something that hasn't finished executing yet. We don't know when it will finish but we assume that it will.
+
+    ```python hl_lines="3 8 10"
+    if __name__ == "__main__":
+        people = None
+        future = None
+        choices = ["list", "update", "clear", "exit"]
+        while True:
+            choice = input(f"Please choose an option [{', '.join(choices)}]: ")
+            if choice == "list":
+                people = list_people(future, people)
+            elif choice == "update":
+                future = ThreadPoolExecutor().submit(update_people, people)
+            elif choice == "clear":
+                people = clear_people(people)
+            elif choice == "exit":
+                break
+            else:
+                print("Invalid choice. Please try again.")
+    ```
+
+21. We need to modify the `list_people` function to handle a future. This ensures that new people will print after an update. Change the following:
+
+    ```python hl_lines="1-4"
+    def list_people(future, people):
+    if future is not None and future.done():
+        people = future.result()
+        future = None
+    print(people)
+    return people
+    ```
+
+22. Save with ++ctrl+s++
+23. Your menu.py should look like this:
+
+    ```python
+    import requests
+    import json
+    from concurrent.futures import ThreadPoolExecutor
+
+    def list_people(future, people):
+        if future is not None and future.done():
+            people = future.result()
+            future = None
+        print(people)
+        return people
+
+    def update_people(people):
+        try:
+            response = requests.get("http://localhost:8000/slow")
+            people = response.json()["data"]
+            print("successfully updated people.")
+        except requests.exceptions.ConnectionError:
+            print("Server is not running. Failed to update.")
+        return people
+
+    def clear_people(people):
+        people = None
+        return people
+
+    if __name__ == "__main__":
+        people = None
+        future = None
+        choices = ["list", "update", "clear", "exit"]
+        while True:
+            choice = input(f"Please choose an option [{', '.join(choices)}]: ")
+            if choice == "list":
+                people = list_people(future, people)
+            elif choice == "update":
+                future = ThreadPoolExecutor().submit(update_people, people)
+            elif choice == "clear":
+                people = clear_people(people)
+            elif choice == "exit":
+                break
+            else:
+                print("Invalid choice. Please try again.")
+    ```
+
+24. Run 
+25. Now run `python menu.py`
+26. Type `update` and press ++enter++. Notice the menu returns instantly.
+27. In a moment you'll see "successfully updated people" print. Type `list` and press ++enter++.
+28. Type `clear` and press ++enter++
+29. Now type `update` and press ++enter++ and quickly type `list` and press ++enter++ before it updates. Notice you can interact with the menu before the result returns!
+30. You've successfully written a multithreaded program. Type `exit` to exit.
+31. Flip back to your django server terminal with the dropdown
+32. Press ++ctrl+c++ to stop the server.
\ No newline at end of file
diff --git a/docs/index.md b/docs/index.md
index abcbd55..09db7fa 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -27,4 +27,8 @@
 
 - "For"
 - Creating an API
-- Reading an API with Python
\ No newline at end of file
+- Reading an API with Python
+
+### [Day 4](day4.md): while
+
+- "While"
\ No newline at end of file
diff --git a/mkdocs.yml b/mkdocs.yml
index 94766e1..26067b7 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -5,6 +5,7 @@ nav:
   - Day 1: day1.md
   - Day 2: day2.md
   - Day 3: day3.md
+  - Day 4: day4.md
 theme:
   name: material
 markdown_extensions: