Intro to Python

Notes on Python Basics

These notes explain some simple ideas in the Python computer language.

What is Python?

• Python is a language that helps us talk to computers.
• We write instructions (code) in Python, and the computer follows them.

Comments: Notes for Humans

• Sometimes we want to write notes in our code just for humans to read.

• The computer ignores these notes. They are called comments.

• Single-Line Comment: Starts with #. The computer ignores everything after # on that line.

  # This is a note for me!
  print("Hello") # This part is also a note

• Multi-Line Comment: Starts and ends with three quotes ("""). The computer ignores everything between them.

  """
  This is a longer note.
  It can span multiple lines.
  The computer will not read this.
  """
  print("Computer reads this!")

Input: Getting Information from the User

• Sometimes we need the computer to ask the user a question and get an answer. This is called input.

• We use the input() instruction for this.

• Example: Asking for your name.

  # Ask the user for their name and store it
  your_name = input("What is your name? ")

  The computer will show “What is your name? ” and wait for you to type something.

Output: Showing Information to the User

• We often want the computer to show us something on the screen. This is called output.

• We use the print() instruction for this.

• Example: Saying hello using the name we got from input.

  your_name = input("What is your name? ")
  print("Hello, ")
  print(your_name) # Shows the name you typed
  print("Nice to meet you!")

  If you typed “Alex”, the computer would show:

  Hello,
  Alex
  Nice to meet you!
  

Data Types: Different Kinds of Information

Computers need to know what kind of information they are working with. These kinds are called data types. Here are a few common ones:

1. String: Text, like words or sentences. Always put quotes (" or ') around strings.

   • Examples: "Hello there", 'cats', "123" (this is text, not a number!)

   greeting = "Hi how are you"
   print(greeting)

2. Integer: Whole numbers. No decimal points allowed. Can be positive, negative, or zero.

   • Examples: 10, -5, 0, 999

   my_age = 15
   print(my_age)

3. Float: Numbers with a decimal point.

   • Examples: 3.14, -0.5, 10.0 (even if the decimal part is zero, the dot makes it a float)

   price = 19.99
   print(price)

4. Boolean: Represents truth values. Can only be True or False. Think of it like “yes” (True) or “no” (False).

   • Examples: True, False

   is_raining = False
   print(is_raining)

• We can ask Python what type a piece of data is using type().

  number = 5
  print(type(number)) # This will show <class 'int'> which means Integer
   
  message = "Good morning"
  print(type(message)) # This will show <class 'str'> which means String