Python - Variable Names

In Python, a variable is a name that represents a value stored in the computer's memory. A variable name is a string of characters that follows certain rules:

1. Variable names can contain letters (both uppercase and lowercase), digits, and underscores (_). They cannot start with a digit.

2. Variable names are case-sensitive, which means that uppercase and lowercase letters are distinct. For example, `myVar` and `myvar` are two different variable names.

3. Variable names cannot be a reserved word in Python. Reserved words are special keywords in Python that have a specific meaning and purpose, such as `if`, `else`, `while`, `for`, `and`, `or`, `not`, etc.

4. Variable names should be descriptive and meaningful, reflecting the purpose of the variable. Avoid using single letters or abbreviations that may be unclear or confusing.

5. Use lowercase letters for variable names, and separate words with underscores to make the name more readable. For example, `my_variable_name`.

Here are some examples of valid and invalid variable names:

Valid variable names:

```

age

name

salary_2021

total_count

```

Invalid variable names:

```

4th_grade   # variable name cannot start with a digit

my-var      # variable name cannot contain hyphens

if          # if is a reserved word in Python

total$count # variable name cannot contain special characters

```

By following these rules, you can create meaningful and easy-to-read variable names that make your code more readable and understandable.