Variables – How Programs Work with Values and Data

In this part of the tutorial you will learn about variables.

A variable in Python points at a place in memory and is assigned to what is stored there. Think of it like a big whiteboard filled with information. A variable points at a specific place on the whiteboard and has the value it points at.

This variable can change value for two reasons.

1. If the variable is pointed at a new value (a new place on the white board),
2. or if the value is changed (someone writes something new at that place in the whiteboard).

Are you ready to try?

• Step 1 Print an assigned value by executing the program (hint: press play symbol)

• Step 2 Try to reassign the variable below the first statement.

• Step 3 Guess what happens before you press execute.
• Step 4 Try to add two variables together by using the new interpreter below.

• Step 5 Then change the first variable to be assigned to “10” (my_first_variable = “10”)

• Lesson: There are types to variables. In the example above you have.
  • my_first_variable = “10” is a string (the quotes “” shows you that)
  • my_second_variable = 20 is an integer

• Step 6: Change the first variable to 6.4 (my_first_variable = 6.4) and press run.

• Lesson: Now the first variable became a float (number with decimal) and the addition worked. That means that an integer and a float can be added together.

• Step 7: Assigning to new variables. See the code below and guess what it will print.

• Step 8: What happens if you change the assignment of c to c = a*b + 3?
• Lesson: While it does not seem as much, but that changed the type of c from a float to an integer. For now you should master the following three primitive types in Python.
  • Integer (int): a = 10
  • Float (float): b = 3.7
  • String (str): c = “Hello”
• Lesson: If you add the following types you get.
  • An integer added to an integer gives an integer (example a = 10 + 20)
  • A float added to an integer gives a float (example: b = 3.4 + 10)
  • A float added to a float gives a float (example: c = -4.8 + 1.9)
  • An integer added to a string gives an error (example: d = 10 + “Hello”)
  • A float added to a string gives an error (example: e = 1.9 + “World”)