A Quick Introduction to Variables

In Python, a variable is essentially a name or a label that refers to a value or stored data. You can think of a variable as a basket in real life used to keep track of information in your program. Variables temporarily store data in the computer’s memory.

Variables are created when they are first assigned a value. An assignment statement creates a new variable and gives it a value. For example, price = 10 creates a variable named price and assigns it the integer value 10. Similarly, x = 6 creates a variable x with the value 6.

A key aspect of Python is its dynamic typing model. Unlike some other programming languages, a variable never has any type information or constraints associated with it. The concept of type lives with objects, not names (variables). Variables are generic and can reference any type of object. This means you can assign a variable to an integer, and later reassign it to a string or a list. For example, A = 10 makes A an integer, but later A = India makes A a string. This allows a variable to store a different value as you continue in your program.

When you use a variable in an expression, it is immediately replaced with the object that it currently refers to. Variables must be assigned before they can be used; trying to use an unassigned variable will result in an error.

There are specific rules for naming variables:

• Variable names can contain both letters (A-Z, a-z) and numbers (0-9).
• They cannot begin with a number.
• The underscore character (_) can appear in a name and is often used in multi-word names (e.g., ram_bank_balance). You must start a variable name with an alphabet or an underscore.
• It is conventional to use only lowercase for variable names.
• You cannot use Python’s reserved words (also called keywords) as variable names. Keywords have a special, fixed meaning in Python.

Python also allows multiple-target assignments, where you can assign a single value to several variables simultaneously. For example, a = b = c = 1 assigns the value 1 to a, b, and c. It’s important to note that with this, there is just one object, and all the variables reference this same object in memory. This behaviour is fine for immutable types like numbers or strings, but can lead to unexpected results with mutable objects like lists, as changes made through one variable will be seen through others referencing the same object.

Finally, you can delete the reference to a variable using the del statement. After a variable is deleted, it is no longer defined.

Programming is often easier if you choose variable names that are self-explanatory.