Introduction to Python

What is Python?

• Really, what IS Python?
• Why are we using Python?
• Have you used Python before? (Hint: Raspberry Pi Minecraft?)

Python (and computer programming) basics

• Syntax
• Data types
• Operators
• Variables 

Syntax

• Basically grammar for computers
• Someone give an example of a grammatically correct ENGLISH sentence!
• Now move around the punctuation and randomize the capitalization and scramble the words
• There's a grammar for every language, including computer language -- it's called syntax!

Basic data types

• String
• Integer
• Float
• Boolean 
• Examples?

Hello World!

• cd into Documents and make a directory named "python_work" and cd into that
• Make a file called "hello_world.py"
• Edit the file and type:
  • print("Hello world!")
• Launch your new program in the terminal!

Operators

• +, -, *, /, %, <, >
• Order of operations anyone?
• Open up your Python interpreter and try it out
  • ex type "python3" into your terminal
  • >>> 5+5*10
• Note: Ctrl+D quits out of the interpreter back into the terminal emulator!

Python excercises

• >>> print("Hello world!")
• Try to solve this math problem by typing one line into the interpreter: 
  • Suppose you do chores once a week, for which you get $5 pocket money, and you have a paper route which you do 5 times a week and get $30—how much money would you earn in a year?

Variables

• In the interpreter type in:
  • >>> fred = 100
  • >>> print(fred)
• We just created a variable, called "fred"
• What is the data type of the variable fred?
• A variable is just something that stores value.
• A variable varies, and can be reassigned. Try:
  •  >>> fred = 200
  • >>> john = fred
  • >>> print(john)

Strings and variables 

• In Python, if you want a variable to hold a string, you need to put quotes around it
  • >>> fred = "this is a string"
  • >>> print(fred) 
• Now, try this:
  • >>> fred = "this is two
  • What did you get?
• Try this:
  • fred = ’’’this is two ... lines of text in a single string’’’

Tricks with strings

• Try this:
  • >>> print(10 * ’a’)
  • >>> print(20 * ’abcd’)
• A "%" can be a placeholder for values:
  • >>> mytext = ’I am %s years old’
  • >>> print(mytext % 12)
• Try this as well:
  • >>> mytext = ’Hello %s, how are you today?’
  • >>> name1 = ’Joe’
  • >>> name2 = ’Jane’
  • >>> print(mytext % name1)

Lists 

• If you wanted to store a shopping list in a variable you could create a string:
  • >>> shopping_list = ’eggs, milk, cheese, celery, peanut butter, baking soda’
  • >>> print(shopping_list)
• Another way we could do that is create an actual list object in Python. Lists are useful for several reasons.
  • >>> shopping_list = [ ’eggs’, ’milk’, ’cheese’, ’celery’, ’peanut butter’]
  • >>>print(shopping_list)
• This is more typing, but it’s also more useful. We could print the 3rd item in the list by using its position (called its index position), inside square brackets []:
  • >>> print(shopping_list[2])

Adding and replacing in lists

• Let's try replacing:
  • >>> shopping_list[3] = ’lettuce’
  • >>>print(shopping_list)
• Now adding to the END of the list:
  • >>> shopping_list.append(’chocolate bar’)
  • >>> print(shopping_list)
• A tuple is a list, but it's immutable. 
  • >>> t = (1, 2, 3)
  • >>> print(t[1])
  • Try to add to a tuple. 
• What does immutable mean?