python-2020-5-day-class/docs/day1.md

Day 1

Before we can dive into our web project we have to cover some Python basics. Let's talk about writing a python program.

The Interactive Python Prompt

1. Make sure you have a (venv) to the left of your terminal cursor. Type python and press enter.

   

2. Type 1+1 and press enter. You should see 2 returned. As long as you see the >>> to the left of your cursor you can type any python code you want and press enter to execute it.

   NOTE: This is not a terminal! You cannot run your django server from here. Before you can do things in the terminal you must exit by typing exit()!

3. Type x=1 and press enter. Nothing should return.

4. Type x and press enter. You should see 1 return. We've give x the value of 1

5. Type x+1 and press enter. You should see 2 returned just like 1+1 above.

6. Type x=3 and press enter. Nothing should return.

7. Type x and press enter. You should see 3 return. Variables in Python can be reassigned to anything else.

8. Type x="hello" and press enter. Nothing should return.

9. Type x and press etner. You should see hello printed to the screen. Variables in python do not have a "type" - they can be integers, strings, floats, etc and can switch between them at will.

10. Type my_name = "\<your name here\>" and press enter. Nothing should return

11. Type my_name and press enter. You should see your name printed to your terminal. my_name is a much better variable name than x. It describes the thing it stores. Please use variable names that are descriptive.

12. Type my_coordinates = (1,2) and press enter. Nothing should return.

13. Type my_coordinates and press enter. (1,2) should return. This is called a tuple. It's useful for storing multiple points of data.

14. Type address = (123, "lane ave", "Columbus", "OH", 43212) and press enter. Nothing should return

15. Type address and press enter. You should see the address print to the terminal. Tuples can hold multiple types of data - 123 is a number and "lane ave" is a string.

16. Type len(address) and press enter. You should see 5 printed to the terminal. There are 5 "things" in the tuple:

    123 (1)

    "lane ave" (2)

    "Columbus" (3)

    "OH" (4)

    43212 (5)

17. Type address[0] and press enter. You should see 123 printed to the terminal. You just accessed the first item in the tuple. Tuples and other collections start at 0 and count up.

18. Type address[1] and press enter. You should see "lane ave" print to the terminal. You just accessed the second item in the tuple

19. Type vocabulary = {"apple": "the usually round, red or yellow, edible fruit of a small tree, Malus sylvestris, of the rose family.", "banana": "a tropical plant of the genus Musa, certain species of which are cultivated for their nutritious fruit."} and press enter. Nothing should return.

20. Type vocabulary and press enter. {"apple": ...} should print to the terminal. This is called a dictionary.

21. Type vocabulary["apple"] and press enter. 'the usually round, red or yellow, edible fruit of a small tree, Malus sylvestris, of the rose family.' should print to the terminal. You just access the definition of apple. Much like tuples can be accessed with address[0] or address[1], dictionary values can be accessed by supplying the keyword, or key for short.

22. Type exit() and press enter. You should no longer see >>> to the left of the cursor.

A Python Program

1. Create a new file called myprogram.py by clicking the "add file" icon in the top left of VSCode.

   

   

   

2. In this file type print('hello, world!') and save with ctrl+S

   

3. In the terminal type python my_program.py and press enter. You should see hello, world! printed to the terminal.

   

4. Congratulations! You ran your first python file. Just like the python command prompt above, running python <filename> on a file with python code in it will execute that python code. Now we can run multiple lines of python at once!

5. Below print('hello, world!') type print('goodbye!)

   

6. Below print('goodbye') type

   x = 1
   y = 2
   print(x + y)
   my_name = "<your name>"
   print(my_name)
   

   

7. In your terminal type python myprogram.py and press enter. You should see

   hello, world!
   goodbye!
   3
   Reese
   

   printed to the terminal

8. This is out of order. We want to print "goodbye" last. Let's fix that with functions.

9. Above print('hello, world!') type def print_hello():

   

10. Indent print('hello, world!') by pressing tab

    

11. Give 'goodbye' the same treatment. This time type def print_goodbye():

    

12. Finally add def middle_stuff(): above the remaining code

    

13. Now type python my_program.py in the terminal and press enter. Nothing will return.

14. We've given our snippets of code "names" by adding a "def" above them. These are called functions. We can call them in any order we want. Let's call them in the correct order by using their names. Add the following to the bottom of my_program.py

    print_hello()
    middle_stuff()
    print_goodbye()
    

    

15. Type python my_program.py in the terminal and press enter. Now everything prints in order!